EN： The Past Perfect tense ('had' + past participle) is used to show that an action was completed before another action in the past. In this sentence, 'had already left' happened before 'got to the stop'.
中文： 过去完成时（had + 过去分词）用于表示在过去某个时间点或另一个过去动作之前，就已经完成的动作。在本句中，「公车已经开走 (had already left)」发生在「我到公交站 (got to the stop)」之前。
By the time we arrived, the movie had started.
在我们到达之前，电影就已经开始了。
EN： The adverb 'already' is commonly used with the Past Perfect tense to emphasize that something happened sooner than expected or before a specific point in time. It is placed between the auxiliary verb 'had' and the past participle.
中文： 副词「already（已经）」常用于过去完成时中，以强调某事比预期更早发生，或在特定时间点之前就已发生。它通常置于助动词「had」与过去分词之间。
I had already finished my homework before dinner.
在晚餐前，我早就已经写完作业了。
EN： Past Perfect Tense (Had + Past Participle) in questions: Used to ask about an action that was completed before another point in the past. In questions, the auxiliary verb 'had' is placed before the subject.
中文： 过去完成时（Had + 过去分词）的疑问句：用于询问在过去某个时间点或动作之前，已经完成的动作。在疑问句中，助动词“had”要置于主语之前。
Had you finished the report before the meeting started?
会议开始前你已经完成报告了吗？
EN： The adverb 'before' at the end of a sentence: Often used with the past perfect tense to mean 'prior to the past time/event being discussed'.
中文： 副词“before”置于句尾：常用于过去完成时，表示“在所讨论的过去时间或事件之前”。
I realized I had never seen him before.
我意识到我以前从未见过他。
EN： The Past Perfect tense ('had' + past participle) is used to describe an action that was completed before another action or a specific point in the past. In this sentence, 'had never missed' indicates that the state of never missing the bus/train occurred prior to 'that day'.
中文： 过去完成时（had + 过去分词）用于描述在过去某个动作或特定时间点之前就已经完成的动作或状态。在本句中，「had never missed」表示「从未错过」这一状态一直持续到「那天」之前。
I had never seen such a beautiful sunset until I visited Greece.
在我去希腊旅游之前，我从未见过如此美丽的日落。
EN： The adverb 'never' is placed between the auxiliary verb 'had' and the main verb (past participle) to express a negative experience up to a past point in time. The prepositional phrase 'until that day' marks the specific boundary in the past when this state changed.
中文： 否定副词「never」（从不）置于助动词「had」与主要动词（过去分词）之间，用来表示截至过去某个时间点为止的否定经验。而介词短语「until that day」（直到那天）则标出过去这个状态发生改变的特定界限。
They had never eaten sushi until they moved to Tokyo.
在他们搬到东京之前，他们从未吃过寿司。
EN： The Past Perfect tense ('had' + past participle) is used to show that an action was completed before another action in the past. In this sentence, 'had started' happened before 'arrived'.
中文： 过去完成时（had + 过去分词）用于表示在过去某个动作或时间点之前就已经完成的动作。在此句子中，「电影开始（had started）」发生在「我们到达（arrived）」之前。
By the time I woke up, my father had already left for work.
当我醒来时，我父亲已经出门去上班了。
EN： The conjunction phrase 'by the time' is used to introduce a time clause, meaning 'no later than the moment that'. It often pairs with the past perfect tense in the main clause to show a sequence of past events.
中文： 连接词短语「by the time」用于引导时间状语从句，意思是「最迟在...的时候」或「当...之时」。它经常与主句中的过去完成时搭配使用，以表示过去事件的先后顺序。
By the time the police arrived, the thief had run away.
当警察到达时，小偷已经逃跑了。
EN： The Past Perfect tense ('had' + past participle) is used to show that an action was completed before another action or a specific time in the past.
中文： 过去完成时（had + 过去分词）用于表示在过去某个动作或特定时间点之前，就已经完成的动作。
By the time we arrived, the movie had started.
在我们到达之前，电影就已经开始了。
EN： The preposition 'before' is used to indicate that an event happened prior to a specific time or event (in this case, 'dinner').
中文： 介词「before」用于表示某事发生在特定时间或事件（在此指「晚餐」）之前。
Please wash your hands before lunch.
午餐前请先洗手。
EN： The Past Perfect tense ('had' + past participle) is used to show that an action was completed before another action or point in time in the past. In this sentence, 'had lost' happened before she 'was sad'.
中文： 过去完成时（had + 过去分词）用于表示在过去某个动作或时间点之前已经完成的动作。在本句中，“弄丢钥匙（had lost）”发生在“难过（was sad）”之前。
He was hungry because he had not eaten lunch.
他那时的很饿，因为他没有吃午餐。
EN： The subordinating conjunction 'because' is used to introduce a clause that states the reason or cause of something. It connects the main clause (the result) with the subordinate clause (the reason).
中文： 从属连词“because（因为）”用于引导表示原因的从属从句。它将主句（结果）与从句（原因）连接起来。
She stayed home because it was raining.
她待在家里，因为那时正在下雨。
EN： The Past Perfect tense ('had' + past participle) is used to show that an action was completed before another action in the past. In this sentence, 'had planned' happened before 'rained'.
中文： 过去完成时（had + 过去分词）用于表示在过去某个时间点或另一个过去动作之前，就已经完成的动作。在此句子中，「规划旅行」（had planned）发生在「下雨」（rained）之前。
I had finished my homework before my mom came home.
在妈妈回到家之前，我已经写完作业了。
EN： The conjunction 'before' is used to connect two clauses, indicating the chronological order of events. The clause following 'before' uses the simple past tense to represent the later event.
中文： 连接词「before」（在……之前）用于连接两个从句，以表示事件的时间先后顺序。接在「before」后面的从句使用一般过去时，代表较晚发生的事件。
They had left the office before the storm started.
在暴风雨开始之前，他们就已经离开办公室了。
EN： The Past Perfect tense ('had' + past participle) is used to show that an action was completed before another action in the past. In this sentence, 'had eaten' happened first, and 'washed' happened second.
中文： 过去完成时（had + 过去分词）用于表示在过去某个动作或时间点之前就已经完成的动作。在此句子中，「吃完饭 (had eaten)」发生在先，「洗碗 (washed)」发生在后。
After she had finished her homework, she watched TV.
在她写完作业后，她看了电视。
EN： Adverbial clauses of time introduced by 'after' describe the sequence of events. When the 'after' clause comes first, it is separated from the main clause by a comma.
中文： 由引导词 'after'（在……之后）引导的时间状语从句，用来描述事件的先后顺序。当 'after' 从句放在句首时，与主句之间必须用逗号隔开。
After we had packed our bags, we left for the airport.
在我们打包好行李后，我们就出发去机场了。
EN： The Past Perfect Tense ('had' + past participle) is used to show that an action happened before another action in the past. In this sentence, 'had forgotten' happened before the action of realizing ('realized').
中文： 过去完成时（had + 过去分词）用于表示某个动作在过去另一个动作或时间点之前已经完成。在本句中，「忘记带伞」（had forgotten）发生在「意识到」（realized）这个过去动作之前。
She realized she had left her phone at home.
她意识到她把手机忘在家里了。
EN： The conjunction 'that' is often omitted in informal English when introducing a noun clause (object clause) after verbs of mental activity like 'realize', 'think', or 'know'. Here, 'I had forgotten my umbrella' is the object clause of 'realized'.
中文： 在非正式英语中，引导名词性从句（宾语从句）的连接词「that」在表示心理活动的动词（如 realize、think、know）后面经常会被省略。在本句中，「I had forgotten my umbrella」是「realized」的宾语从句。
I knew (that) you would come.
我知道（那时）你一定会来。
EN： The Past Perfect tense ('had' + past participle) is used to show that an action was completed before another action in the past. In this sentence, 'had cleaned' happened before 'came'.
中文： 过去完成时（had + 过去分词）用于表示在过去某个动作或时间点之前就已经完成的动作。在本句中，「打扫房间 (had cleaned)」发生在「我们到来 (came)」之前。
I had finished my homework before dinner.
我在晚餐前就已经做完作业了。
EN： The conjunction 'before' is used to connect two clauses, indicating that the action in the main clause (Past Perfect) occurred prior to the action in the subordinate clause (Simple Past).
中文： 从属连词「before (在...之前)」用于连接两个从句，表示主句的动作（过去完成时）发生在从句的动作（一般过去时）之前。
We had planned the trip before it rained.
在下雨之前，我们就已经规划好这次旅行了。
EN： The Past Perfect Tense (had + past participle) is used to describe an action or experience that occurred before a specific point in the past. In this sentence, 'had never seen' indicates that the experience of seeing such a crowd did not happen at any point prior to that past moment.
中文： 过去完成时（had + 过去分词）用于描述在过去某个特定时间点之前已经发生或未曾发生的动作或经验。在此句子中，「had never seen」表示在过去的那个时刻之前，从未有过看见如此庞大人群的经验。
I had never tasted sushi before I went to Japan.
在我去日本之前，我从未尝过寿司。
EN： 'Such a/an + adjective + singular countable noun' is a structure used for emphasis, meaning 'of this/that kind' or 'so great'. It intensifies the description of the noun.
中文： 「such a/an + 形容词 + 单数可数名词」是用于加强语气的结构，意为「如此的...」或「这样特别的...」，用来强化对该名词的描绘。
It was such a beautiful day that we decided to go for a picnic.
那是如此美好的一天，以至于我们决定去野餐。
EN： The Past Perfect tense ('had' + past participle) is used to show that an action was completed before another action in the past. In this sentence, 'had saved' happened before the past action 'crashed'.
中文： 过去完成时（had + 过去分词）用于表示在过去某个动作或时间点之前就已经完成的动作。在此句子中，「保存 (had saved)」发生在另一个过去动作「崩溃 (crashed)」之前。
By the time we arrived, the movie had started.
在我们到达之前，电影就已经开始了。
EN： The subordinating conjunction 'before' is used to connect two clauses, indicating the chronological order of events. The event in the 'before' clause happens second.
中文： 从属连词「before（在……之前）」用于连接两个从句，以表示事件发生的先后顺序。在 before 从句中的事件较晚发生。
I had finished my homework before dinner.
我在晚餐前就已经做完作业了。
EN： The verb 'plan' is followed by a to-infinitive (to + base verb) to express an intention or a future action that was decided upon.
中文： 动词“plan”（计划）后面须接不定式（to + 动词原形），用来表示意图或决定要做的未来行动。
We planned to visit the museum, but it was closed.
我们计划去参观博物馆，但它关门了。
EN： The simple past tense ('planned') is used here to describe a completed action or state of mind that occurred at a specific time in the past ('Last Sunday').
中文： 此处使用一般过去时（“planned”）来描述在过去特定时间（“上星期天”）所发生且已完成的动作或心态。
Last night I decided to stay home.
昨晚我决定留在家里。
EN： The Past Perfect tense ('had' + past participle) is used to show that an action was completed before another action in the past. In this sentence, 'had stayed up' happened before the past action 'woke up'.
中文： 过去完成时（had + 过去分词）用于表示在过去某个动作或时间点之前已经完成的动作。在本句中，“熬夜”（had stayed up）发生在“起床”（woke up）这个过去动作之前。
I woke up late because I had stayed up too long the night before.
我起床晚了，因为我前一天晚上熬夜太久。
EN： The phrasal verb 'stay up' means to go to bed later than usual. It is often followed by 'late' or 'too long' to describe the duration.
中文： 短语动词“stay up”意为“熬夜”或“比平时晚睡”。通常后接“late”（晚）或“too long”（太久）来描述持续的时间。
She stayed up late to study for her final exam.
她为了准备期末考试而熬夜到很晚。
EN： The Past Perfect tense ('had' + past participle) is used to show that an action was completed before another action in the past. In this sentence, 'had already left' happened before 'reached'.
中文： 过去完成时（had + 过去分词）用于表示在过去某个时间点或动作之前，就已经完成的动作。在本句中，“火车已经开走（had already left）”发生在“我到达车站（reached）”之前。
By the time we arrived at the theater, the movie had already started.
当我们到达电影院时，电影已经开始了。
EN： The conjunction phrase 'by the time' is used to establish a deadline or a point in time by which something else has occurred. It is typically followed by a simple past verb, while the main clause uses the past perfect.
中文： 连词短语“by the time”（到了…的时候）用于设定一个时间点或截止时间，在此时间点之前另一件事已经发生。后面通常接一般过去时动词，而主句则使用过去完成时。
By the time he finished his homework, everyone had gone to bed.
当他写完作业时，大家都已经上床睡觉了。
EN： The Past Perfect tense ('had' + past participle) is used to describe an action that was completed before another action or point in time in the past. Here, 'had never missed' happened before the past action 'felt'.
中文： 过去完成时（had + 过去分词）用于描述在过去某个动作或时间点之前就已经完成的动作。在此句中，「从未错过」（had never missed）发生在过去的动作「感到」（felt）之前。
She had already eaten dinner when I arrived.
当我到达时，她已经吃过晚餐了。
EN： The coordinating conjunction 'so' is used to introduce a clause that shows the result or consequence of the preceding clause.
中文： 并列连词「so」（所以）用于引导一个表示前面从句结果或影响的从句。
It was raining, so we stayed indoors.
那时正在下雨，所以我们待在室内。
EN： In many English-speaking countries, public transportation schedules (like trains) are expected to be punctual. Missing a train can cause significant delays in one's daily schedule, which explains the strong emotional reaction ('very upset') of the speaker.
中文： 在許多英語系國家，大眾運輸工具（如火車）通常被要求要準點。錯過火車可能會對個人的日常行程造成重大延誤，這解釋了說話者為何會有如此強烈的情緒反應（「非常沮喪」）。
EN： The Past Perfect Tense ('had' + past participle) is used to show that an action was completed before another action in the past. In this sentence, 'had not checked' happened before the past action 'remembered'.
中文： 过去完成时（had + 过去分词）用于表示在过去某个动作或时间点之前已经完成的动作。在此句子中，「没有确认过（had not checked）」发生在过去动作「想起（remembered）」之前。
I realized that I had left my keys at home.
我意识到我把钥匙忘在家里了。
EN： A noun clause starting with 'that' can function as the direct object of a transitive verb (like 'remembered'). The conjunction 'that' is often omitted in casual speech but is kept here for clarity.
中文： 由连接词「that」引导的名词性从句可以作为及物动词（如「remembered」）的直接宾语。在口语中「that」常被省略，但在此处保留以使语义更清晰。
She remembered that she had an appointment today.
她想起她今天有一个预约。
EN： Indirect speech (reported speech) is used to report what someone else said. When the reporting verb (e.g., 'told') is in the past tense, the tenses in the reported clause usually shift back (backshift). Here, the original spoken words 'Another train has not come yet' (present perfect) shift to the past perfect 'had not come yet'.
中文： 间接引语（转述语气）用于转述他人所说的话。当主要动词（如 'told'）为过去式时，被转述从句中的时态通常需要往回推一个时态（时态后退）。在此句中，原本说话的内容「另一班火车还没来」（现在完成时）转述后变成了过去完成时「had not come yet」。
She told me that she had already finished her work.
她告诉我她已经完成工作了。
EN： The past perfect tense ('had' + past participle) is used to show that an action happened before another action in the past. In this sentence, the train's failure to arrive ('had not come') happened before the worker spoke ('told').
中文： 过去完成时（had + 过去分词）用于表示在过去某个动作或时间点之前就已经发生或未发生的动作。在本句中，火车还没来（had not come）的状态发生工作人员告知（told）之前。
By the time I arrived at the station, the train had already left.
当我到达车站时，火车已经开走了。
EN： The Past Perfect tense ('had' + past participle) is used to describe an action that was completed before another action or state in the past. In this sentence, 'had given up' happened before the state of being glad ('was').
中文： 过去完成时（had + 过去分词）用于描述在过去某个动作或状态之前就已经完成的动作。在本句中，“已经放弃”（had given up）发生在“感到高兴”（was glad）之前。
She was disappointed because she had lost her keys.
她很失望，因为她弄丢了钥匙。
EN： The adverb 'almost' is used to indicate that something was very close to happening but did not actually happen. In past perfect constructions, it is placed between the auxiliary verb 'had' and the past participle.
中文： 副词“almost”（几乎）用于表示某事差一点就发生，但实际上并未发生。在过去完成时的结构中，它位于助动词“had”与过去分词之间。
I had almost finished my homework when the power went out.
停电时，我几乎快要写完作业了。
EN： The Past Perfect tense (had + past participle) is used to show that an action was completed before another action in the past. In this sentence, 'had waited' occurred before the past action of 'arrived'.
中文： 过去完成时（had + 过去分词）用于表示在过去某个动作或时间点之前已经完成的动作。在本句中，“已经等待（had waited）”发生在过去的动作“到达（arrived）”之前。
By the time the movie started, we had already bought our popcorn.
在电影开始之前，我们就已经买好爆米花了。
EN： The adverb 'finally' is used to emphasize that something happened after a long time or after some difficulty, usually placed before the main verb.
中文： 副词“finally（终于）”用来强调某事在经历了很长时间或困难之后才发生，通常置于主要动词之前。
After searching for an hour, she finally found her keys.
找了一个小时后，她终于找到了她的钥匙。
EN： In English-speaking cultures, punctuality is highly valued. Arriving an hour late for a meeting with friends is generally considered a significant delay, which is why the speaker uses the past perfect tense to emphasize the long duration their friends had to wait before the arrival.
中文： 在英語系國家中，守時是一項非常重要的社交禮儀。與朋友聚會遲到一個小時通常被視為嚴重的耽擱，這也是為什麼說話者使用過去完成式來強調朋友們在自己抵達之前，已經無奈地等待了極長的時間。
EN： The verb 'learn' can be followed by a noun clause starting with 'that' (often omitted in informal speech) which functions as the direct object, expressing the fact or information that was acquired.
中文： 动词「learn」（学习、得知）后面可以接由「that」引导的名词性从句（在口语中常省略）作为直接宾语，用来表示所学到或得知的具体事实或信息。
She learned that honesty is the best policy.
她学到了诚实是上策。
EN： The modal verb 'should' is used to express duty, advice, or recommendation. In this sentence, it indicates a wise or necessary action to take.
中文： 情态动词「should」用来表示义务、建议或劝告。在本句中，它表示一个明智或有必要采取的行动。
You should drink more water every day.
你每天应该多喝水。
EN： Wh-questions with the verb 'to be' in the past simple tense. In this structure, the question word (Why) is followed by the past tense form of 'be' (were), then the subject (you), and finally the adjective/complement (late).
中文： 使用过去时 be 动词的 Wh- 问句。在此结构中，疑问词 (Why) 后面接 be 动词的过去式 (were)，接着是主语 (you)，最后是形容词/补语 (late)。
Why were you angry yesterday?
你昨天为什么生气？
EN： Adverbials of time like 'this morning' are used to specify when an action or state occurred in the past. They usually appear at the end of the clause.
中文： 时间副词（如 'this morning'）用于明确指出过去某个动作或状态发生的时间，通常置于从句的末尾。
I saw him this morning.
我今天早上看到他了。
EN： In English-speaking cultures, asking 'Why were you late?' in a casual or friendly tone among peers (like Sarah to Ryan) is common and shows friendly concern rather than strict interrogation. Adding the person's name at the end softens the question.
中文： 在英語系國家中，同儕之間（如莎拉對萊恩）以輕鬆或友善的語氣詢問「你為什麼遲到？」是很常見的，這通常代表友善的關心，而非嚴厲的審問。在句末加上對方的名字（萊恩）能使語氣顯得更溫和。
EN： The Past Perfect tense (had + past participle) is used to show that an action was completed before another action in the past. In this sentence, 'had left' happened before 'got there'.
中文： 过去完成时（had + 过去分词）用于表示在过去某个动作或时间点之前就已经完成的动作。在此句中，“公车开走（had left）”发生在“我到达那里（got there）”之前。
The movie had already started when we arrived at the theater.
当我们到达电影院时，电影已经开始了。
EN： The conjunction 'before' is used to connect two clauses, indicating the chronological order of events. The clause following 'before' usually uses the Simple Past tense.
中文： 从属连词“before（在……之前）”用于连接两个从句，以表示事件发生的先后顺序。紧跟在 before 后面的从句通常使用一般过去时。
I had finished my homework before I went to bed.
我在睡觉前就已经做完作业了。
EN： The Past Perfect tense ('had' + past participle) is used to show that an action was completed before another action or a specific time in the past.
中文： 过去完成时（had + 过去分词）用于表示在过去某个动作或特定时间点之前，就已经完成的动作。
By the time we arrived, the movie had started.
在我们到达之前，电影就已经开始了。
EN： The preposition 'before' is used to indicate that an event happened prior to a specific point in time or another event.
中文： 介词「before」用于表示某个事件发生在特定时间点或另一个事件之前。
I had finished my homework before dinner.
我在晚餐前就已经做完了作业。
EN： The Past Perfect Tense (had + past participle) is used to describe an action that was completed before a specific point in time in the past. In this question, 'had you been' refers to the period before 'last week'.
中文： 过去完成时（had + 过去分词）用于描述在过去某个特定时间点之前已经完成的动作。在此问句中，“had you been”指的是在“上周”这个时间点之前发生的状态。
Had you finished the report before the meeting started?
在会议开始之前，你已经完成报告了吗？
EN： The adverb 'ever' is commonly used in past perfect questions to mean 'at any time before the specified past time'. It is placed between the subject and the past participle.
中文： 副词“ever”（曾经）常用于过去完成时的问句中，表示“在过去指定时间之前的任何时候”。它通常置于主语与过去分词之间。
Had they ever met him before that night?
在那天晚上之前，他们曾见过他吗？
EN： In English-speaking cultures, asking about someone's past travels or experiences using the Past Perfect is common when establishing a timeline of events, especially when discussing a specific past trip or event that occurred recently.
中文： 在英語系國家中，當要釐清過去事件的時間軸時（特別是討論到最近發生的某次旅行或事件），使用過去完成式來詢問對方在此之前的經歷是非常常見且自然的表達方式。
EN： The Past Perfect tense (had + past participle) is used to describe an action that was completed before another action or a specific time in the past. In this sentence, 'had never visited' indicates that the action of visiting did not happen at any point prior to the past reference point.
中文： 过去完成时（had + 过去分词）用于描述在过去某个动作或特定时间点之前就已经完成的动作。在此句子中，「had never visited」表示在过去的那个时间点之前的任何时候，都从未发生过拜访该地的行为。
I had already finished my homework when my friend called me.
当我朋友打电话给我时，我已经做完作业了。
EN： The adverb 'never' is used to express negation meaning 'at no time'. In the past perfect tense, 'never' is placed between the auxiliary verb 'had' and the past participle (visited). The word 'before' is used at the end of the sentence to reinforce the idea of 'prior to that past time'.
中文： 否定副词「never」用于表示「从未、绝不」。在过去完成时中，「never」置于助动词「had」与过去分词（visited）之间。句尾的「before」则用来强调「在过去的那个时间点之前」的概念。
She had never seen a glacier before she went to Alaska.
在她去阿拉斯加之前，她从未见过冰川。
EN： The Past Perfect tense ('had' + past participle) is used to show that an action was completed before another action in the past. In this sentence, 'had read' happened before 'began'.
中文： 过去完成时（had + 过去分词）用于表示在过去某个动作或时间点之前，已经完成的动作。在本句中，「已经读完 (had read)」发生在「课堂开始 (began)」之前。
By the time the movie started, we had already bought our popcorn.
在电影开始之前，我们就已经买好爆米花了。
EN： The phrase 'by the time' is a subordinating conjunction used to introduce a time clause, meaning 'no later than the moment that'. It is commonly paired with the past perfect in the main clause.
中文： 短语「by the time」是一个从属连词，用来引导时间状语从句，意思是「最迟在...之时」或「到...的时候」。主句通常搭配过去完成时使用。
By the time he arrived at the station, the train had left.
到他抵达车站时，火车已经开走了。
EN： The Past Perfect tense ('had' + past participle) is used to show that an action was completed before another action in the past. In this sentence, 'had run' happened before the past state of feeling tired ('felt').
中文： 过去完成时（had + 过去分词）用于表示在过去某个动作或时间点之前已经完成的动作。在本句中，「跑了很久」（had run）发生在「感到疲倦」（felt）这个过去状态之前。
She was hungry because she had not eaten breakfast.
她肚子饿是因为她没有吃早餐。
EN： The subordinating conjunction 'because' is used to introduce a clause that states the reason or cause for the action in the main clause.
中文： 从属连词「because」（因为）用于引导一个表示原因或理由的从句，用来解释主句动作发生的原因。
They stayed home because it was raining.
他们待在家里是因为正在下雨。
EN： The Past Perfect tense (had + past participle) is used to show that an action was completed before another action in the past.
中文： 过去完成时（had + 过去分词）用于表示在过去某个动作或时间点之前，已经完成的动作。
I had finished my homework before my mom came home.
在妈妈回到家之前，我已经写完作业了。
EN： The conjunction 'before' is used to connect two clauses, showing the chronological order of events. The action in the 'before' clause happens second and is in the simple past tense.
中文： 连接词「before」（在……之前）用于连接两个从句，以显示事件的时间顺序。在「before」引导的从句中的动作较晚发生，须使用一般过去时。
He washed his hands before he ate dinner.
他在吃晚餐之前洗了手。
EN： The Past Perfect tense ('had' + past participle) is used to show that an action was completed before another action in the past. In this sentence, 'had studied' happened before 'knew'.
中文： 过去完成时（had + 过去分词）用于表示在过去某个动作或时间点之前，就已经完成的动作。在此句子中，「努力读书 (had studied)」发生在「知道答案 (knew)」之前。
She had already left when I arrived at the station.
当我到达车站时，她已经离开了。
EN： The subordinating conjunction 'because' is used to introduce a clause that states the reason or cause for the action in the main clause.
中文： 从属连词「because（因为）」用来引导一个表示原因的从句，说明主句动作发生的原因。
We stayed indoors because it was raining heavily.
因为雨下得很大，所以我们待在室内。
EN： The Past Perfect tense ('had' + past participle) is used to show that an action was completed before another action in the past. In this sentence, 'had packed' happened before 'left'.
中文： 过去完成时（had + 过去分词）用于表示在过去某个时间点或动作之前已经完成的动作。在本句中，「打包（had packed）」发生在「出发（left）」之前。
After she had finished her homework, she watched TV.
在她写完作业之后，她看了电视。
EN： The phrasal verb 'leave for' means to depart in order to go to a specific destination. 'Leave for the trip' means to start the journey.
中文： 短语动词「leave for」表示出发前往某个特定的目的地。「leave for the trip」意指启程去旅行。
They left for the airport early in the morning.
他们一大早就出发去机场了。
重要单词附有 IPA 发音、定义、例句和互动式测验。
在本文中： 意识到、明白、领悟
在本文中： 幸好、幸运地
在本文中： （电脑系统或程序）死机、崩溃
在本文中： 难过的、沮丧的、生气的
在本文中： 时刻表、日程表
在本文中： 截止日期、最后期限
在本文中： 人群、群众
在本文中： 准备、预备
片语包含类型标示、双语定义、用法说明和例句。
To go to bed later than usual.
熬夜、不睡觉
To stop believing that something good will happen or that you will succeed.
放弃希望
Used to say that something has already happened when something else happens.
到了…的时候、在…之前