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When + do/does/did + subject + verb?
疑问副词，询问时间。
When did you arrive?
你什么时候到的？
……的时候；届时
先理解核心含义，再看它在真实句子里的用法。
……的时候；届时
The time at, on, or during which.
When did you arrive?
你什么时候到的？
用于引导表示时间的定语从句。
在较早时候且处于不同(通常较不利)的情况下。
At an earlier time and under different, usually less favorable, circumstances.
所述的时间。
The time at, on or during which.
That was the year when my family moved to a new city.
那是我们一家人搬去新城市的那一年。
I miss the days when we used to play outside until dark.
我怀念我们常常在外面玩到天黑的日子。
Do you remember the exact moment when the lights went out?
你还记得灯熄灭的那个确切时刻吗？
疑问副词，询问时间。
When did you arrive?
你什么时候到的？
定语从句中用作关系副词。
I remember the day when we first met.
我记得我们第一次见面的那一天。
引导时间状语从句。
When I was young, I loved to play outside.
我小时候喜欢在外面玩。
Not this
When I will go to Beijing, I will visit you.
Use this
When I go to Beijing, I will visit you.
时间状语从句中，用一般现在时表示将来，不用will。
Not this
I was cooking when she was watching TV.
Use this
I was cooking while she was watching TV.
当两个动作同时持续发生时，应用while引导时间状语从句，强调同时进行；when通常用于一个动作发生时另一个动作突然发生。
Focus on the distinctions below. Other candidates are kept compact until a reliable usage note is available.
什么时候；何时
I don't know when to start.
我不知道什么时候开始。
当谈到；就……而言
When it comes to cooking, she is an expert.
谈到烹饪，她是专家。
必要时
Add more water when necessary.
必要时加更多水。
即使当；即使……的时候
He keeps smiling even when he is sad.
即使难过时他也保持微笑。
可能时
Take the stairs when possible.
可能时走楼梯。
从什么时候起
Since when have you been here?
你从什么时候起在这里的？
绝无可能
Sure, he'll clean his room when pigs fly.
当然，他绝不可能收拾房间。
当谈到…时；在…方面
When it comes to cooking, she is an expert.
谈到烹饪，她是专家。
入乡随俗
When in Rome, do as the Romans do, so learn to use chopsticks in China.
入乡随俗，在中国要学会用筷子。
当你向星星许愿时，你的梦想就会成真。
When you wish upon a star, anything is possible.
当你向星星许愿时，一切皆有可能。
当我离开你时，我只是个学徒；现在我是大师了。
When I was young, I never understood the power of this line.
当我年轻时，我从不理解这句台词的力量。
Use when naturally, then get feedback on meaning, tone, grammar, and phrasing.
Revisit a common error or keep this word in your review list.
问时间就用'when'，'w'像疑问的'问'。
通常用于询问时间，语体中性，适用于口语和书面语。
常用于疑问句或引导从句，表示时间。
Dictionary facts from AI_FALLBACK, DICTIONARY_API_DEV, ECDICT, WIKTIONARY.