If I had met him before, I could recognize him.要是我以前遇见过他，我就能认出他了。

　　（从句表示与过去事实相反，主句表示与现在或将来事实相反）

　　If we were driving at a speed of 100 Li an hour, we would have arrived there 2 hours ago. 如果我们的行车速度每小时100里，两小时以前我们就会到达那里了。

　　（从句与现在事实相反，主句与过去事实相反）

　　Example:

　　If you _____ that late movie last night, you wouldn’t be sleepy.

　　A. haven’t watched            B. didn’t watch

　　C. hadn’t watched             D. wouldn’t have watched

　　5． 省略连词if

　　在条件状语从句中，如果有were, should, had，可以把连词if 省去，把 were, should, had 放在句首，构成条件意义。例如：

　　Should it rain tomorrow, what would you do? 万一明天下雨，你怎么办？

　　Were there no friction, we could not walk. 要是没有摩擦力，我们就不能行走。

　　Had we known about the new method, we should have applied it earlier.

　　如果我们过去知道这种新方法，我们早就应用了。

　　Example:

　　Had Alice been more hardworking, she _______.

　　A. had not failed           B. would not fail

　　C. could not be failed       D. would not have failed

　　_______ today, he would get there by Friday.

　　A. Would he leave         B. Was he leaving

　　C. Were he to leave        D. If he leaves

　　______ difficulties, we would be successful.

　　A. Should we overcome     B. Would we overcome

　　C. Might we overcome      D. Could we overcome

　　6.       虚拟结构中省略主句或从句

　　虚拟结构中有时可省去主句或从句，并不影响意义的完整。

　　(1)省去条件从句

　　That would be fine. 那太好了。（省去了if you would come 或类似条件）

　　I wouldn’t pass up the chance to visit China. 我不会放弃访问中国的机会。

　　We might have produced more coal. 我们可能生产出更多煤炭。

　　注：省略条件句，在试题中很少见到。

　　(2)省去主句，常用以表示愿望。从句谓语多用过去时或过去完成时。

　　If only she were here. 假如她在这儿该多好啊！

　　If only he lived! 假如他活着该多好啊！

　　If only I had known it before. 如果我早先知道这件事，那就好了。

　　Example:

　　If only it _____! but it is too late.

　　A. is avoided   B. has avoided   C. could be avoided   D. can be avoided

　　If only everything _____ out as we wanted it to in life!

　　A. is working   B. worked     C. works      D. has worked