托福语法学习：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。
1 O! M- \, k/ {- Q& z( D　　If I had known that you were coming I would have met you at the air－port．
6 f1 e  j0 Y1 c! u, ]7 @; k　　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。）
, [% M$ \4 N/ J3 k7 ^　　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
　　1 可以用could或might而不用would：
" p. K2 q+ m0 ^1 J2 c　　If we had found him earlier we could have saved his life．
+ R! U& n8 F1 r/ x) R0 g　　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．
% C; t) R5 e9 Y! j0 D: E. s  q% ^　　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）
　　If our documents had been in order we could have left at once．
9 X6 ]: d4 n+ q2 F0 ?; C+ r  k　　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：
3 h1 P' `) q  A4 k　　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。
" ?/ O# V. [+ X, E* i　　3 可以在if从句中用过去完成进行时：
. S7 e9 O. m+ C* Y　　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。
  U4 L5 O6 j- q" I9 {! }　　4 可以把类型2和类型3结合起来：
　　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．
, e2 f, s+ B$ c5 l  ?' y　　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
7 t0 c5 W5 `% Y2 u1 N4 K　　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。）
( ~, h7 @; H( R- Z# |: E2 i4 `　　5 had可以位于句首并省略if：
　　If you had obeyed orders this disaster would not have happened．相当于：
　　Had you obeyed orders this disaster would not have happened．
$ x6 t+ b! v8 |( l5 @6 {: [+ L/ \　　要是你当时服从了命令，这场灾难就不会发生了。