I was writing a letter while she came in.
老师告诉上句中的 while 应改为 when。我不理解为什么要作这样的修改, when 和 while
不是都作“当……的时候”解吗？
上句中的 while 必须改为 when, 因为 when 和 while 虽然都可译作“当……的时候”, 但它们的用法是有区别的:
A. when 引导的时间状语从句既可表示时间位置(time position)，也可表示时间的延续，即表示一段时间(duration)。因此 when 从句既可使用瞬间动词(如 arrive, begin, borrow, lend, go, come, take, leave, stop, finish, die, join)，也可使用持续动词(be, lie, stay, live, study):
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John was having his dinner when I saw him. 当我看到约翰的时候,他正在吃饭。
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I bought the car when I received my first salary. 当我得到第一次工资的时候,我便买了这辆汽车。
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She can write only when the baby is asleep. [ = while ] 只有婴儿睡着的时候,她才能写作。
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I was fond of swimming when I was yet a child. 当我还是个孩子的时候,我就喜欢游泳。
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My pen dropped on the ground when I was walking in the park. 当我在公园散步的时候,我的笔掉在地上了。
B. while 引导的时间状语从句表示时间的延续, 即表示一段时间, 而不是瞬间, 因此, 不能与瞬间动词连用, 如上题中的 come:
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We must strike while the iron is hot. 要趁热打铁。
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While we were talking, the teacher came in. 我们正在谈话的时候，老师走了进来。不难发现，when 有时可用来代替 while，而 while 却不能用来代替 when 的第一种用法。
when 与 while 的另一个区别: when 从句的动作既可与主句的动作同时发生, 亦可先后发生, 而 while 从句只能表示主句的动作发生在 while 从句所表达的时间段之内:
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When you telephoned me, I was drawing a picture. 你给我打电话的时候，我正在画画。
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Tom was disappointed that most of the guests had left when he arrived at the party. (先后发生)(全国高考) 汤姆很扫兴的是,他到达聚会地时,大部分客人都已经走了。
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My brother fell while he was riding his bicycle ... (同时发生)(全国高考) 我弟弟骑自行车时跌倒了……
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The telephone rang while I was having a shower. 我正在淋浴的时候,电话铃响了。请做下面的英语试题:
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____ Betty came home yesterday evening, the children were watching TV.
A. While B. As soon as C. When D. Whenever(全国高考,96)
- ____ I got there, Mr. Black was reading a telegram from his hometown. He seemed excited.
A. When B. As C. While D. Since(北京会考,95-20)