Unit 5 Period 3.ppt
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Period Three　Grammar
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一、时间状语从句
1．引导时间状语从句的连词有when，while，as，before，after，whenever，till，until，since，once等。
When we lived in town，we often went to the theatre.
当我们住在城里时，我们常常去看戏。
After she got married，she changed completely.
结婚之后她完全变了。
状语从句
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Whenever she had a cold，she ate only fruit.
每当感冒时，她就只吃水果。
I have written home four times since I came here.
自从我到这儿来，我往家写了四封信。
Once you remember it，you'll never forget it.
你一旦记住了它，就永远不会忘记。

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2．when除了作“当……时候”解之外，还有“那时(突然)，这时(突然)”之意，常用于下列句式：was/were doing...when...“正……突然……”；was/were about to/going to do...when...“正要……突然……”；had just done...when...“刚……突然就……”。

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We were having a meeting when someone broke in.
我们正开会突然闯进一人。
We were about to set off on our way when it suddenly began to rain.
我们刚要出发，突然下雨了。
另外，when还可作“既然”解，引出原因状语从句。
It was foolish of you to take a taxi when you could easily walk there in five minutes.
既然能轻易地五分钟内步行到那儿，那么乘坐出租车你太傻了。
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3．before“在……之前”，还可译为“还未……就……”；“不到……就……”；“……才……”；“