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类别 |
用法 |
例句 |
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If引导的条件从句 |
与现在事实相反 |
从句动词：过去式（be用were）
主句动词：should/would/could/might+动词原形 |
If he were here, he would help us. |
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与过去事实相反 |
从句动词：had+过去分词
主句动词：should/would/could/might+have+过去分词 |
If I had been free, I would have visited you. |
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与将来事实相反 |
从句动词：过去式/ should+动词原形/ were+不定式
主句动词：should/would/could/might+动词原形 |
If it should rain tomorrow, we would not go camping. |
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其它状语从句 |
as if引导的状语从句中动词用过去式或过去完成式 |
They are talking as if they had been friends for years. |
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in order that / so that引导的状语从句中动词用can / could / may / might / would等+动词原形 |
Turn on the light so that we can see it clearly. |
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宾语从句 |
demand, suggest, order, insist后接的从句中动词为should+动词原形 |
He suggested that we not change our mind. |
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wish后的从句中分别用过去式，过去完成式和should/would+动词原形表示与现在，过去和将来情况相反 |
I wish I could be a pop singer.
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主语从句 |
在It is necessary / important / strange that…, It is suggested / demanded / ordered / requested that… 等从句中，谓语动词用should+动词原形 |
It is strange that such a person should be our friends. |
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其它句型中 |
It is time that…句型中动词用过去式或should+动词原形 |
It’s high time that we left. |
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would rather所接的从句中动词用过去式或者过去完成式 |
I would rather you stayed at home now. |
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If only句型中动词常用过去式或者过去完成式，表示强烈的愿望 |
If only our dream had come true! |
