托福语法技巧：条件句类型3

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　　if从句中的动词用过去完成时，主句中的动词用条件完成时。这种句子所指的时间是过去；所提出的条件是不可能实现的，因为if从句中的动作在过去并未发生。
* e3 ?$ v& S' n4 A5 H1 z) M: H- ]　　If I had known that you were coming I would have met you at the air－port．
　　要是我早知道你要来的话，我就会在机场接你了。（但我不知道，所以我也没去。）
' \+ {: u* x; v　　If he had tried to leave the country he would have been stopped at the frontier．
　　要是他当时试图离开这个国家，他就会在边界被阻拦。（但他并未这样做。）
　　基本形式可能的变化形式
; {* M' ^# L7 o+ C$ Q! T6 Z/ O　　1 可以用could或might而不用would：
8 {& U$ ^: e/ V: k8 V, c* P) L4 d　　If we had found him earlier we could have saved his life．
　　要是我们那时早点找到他的话，我们会把他救活的。（能力）
　　If we had found him earlier we might have saved his life．
% z. S* E2 _( I  n! B1 y$ a　　要是我们那时早点找到他的话，我们可能会把他救活的。（可能性）
* H# k$ K& ^' i& M# @1 [5 G# A' G　　If our documents had been in order we could have left at once．
　　要是我们的证明文件都齐备的话，我们那时就能够马上走。（能力或允许）
　　2 可以用条件完成进行时：
" k% C3 G: o& M　　At the time of the accident I was sitting in the back of the car，because Tom’s little boy was sitting beside him in front．If Tom’s boy had not been there I would have been sitting in front．
　　事故发生的时候，我坐在车子的后座，因为汤姆的小儿子坐在前边他的身旁。要是汤姆的孩子没坐在那里的话，我就会坐在前面了。
　　3 可以在if从句中用过去完成进行时：www.Examw.com
　　I was wearing a seat belt．If I hadn’t been wearing one I’d have been seriously injured．
　　我当时系了安全带。要是没有系上的话，我就会受重伤了。
　　4 可以把类型2和类型3结合起来：
5 i, \6 y' }: m6 @　　The plane I intended to catch crashed and everyone was killed．If I had caught that plane I would be dead now／I would have been killed．
, k- {7 U% F3 B% b, P; ~　　我原想赶乘的那架飞机坠毁了，所有乘客都遇难身亡。要是我赶上了那架飞机，我也就没命了／我就会摔死了。（类型 3）
　　If I had worked harder at school I would be sitting in a comfortable office now；I wouldn’t be sweeping the streets．
　　要是在上学时学习再努力一些，我现在就会坐在舒适的办公室里，而
/ C) u5 ]+ [$ y# B5 E$ Y; m) f9 _, a　　不会是在扫大街了。（但我上学时不努力，因而我现在在扫大街。）
4 I$ C( E! Y* ~0 U8 ~& G+ W2 C　　5 had可以位于句首并省略if：
6 X" \, ]' q' p　　If you had obeyed orders this disaster would not have happened．相当于：
　　Had you obeyed orders this disaster would not have happened．
　　要是你当时服从了命令，这场灾难就不会发生了。