If +主语 +动词过去式 主语+ would, should, could, might+原形动词
If I feared death, I wouldn't be a communist.
If there were no air, we couldn't live.
I would ask George to lend us the money if I ______ him.
A. had known B. knew C. have known D. know
I _____ it to him if I thought he would understand.
A. shall explain B. will explain C. would explain D. explain
If + 主语 + 动词过去完成式 主语 + would, should, could, might+have + 过去分词
If you had come a few minutes earlier, you would have met him.
If there had been no air in the tube, the result of the experiment would have been more accurate.
If you hadn't gone with Tom to the party last night, _______.
A. you would meet John already
B. you won't have missed John
C. you will have met John
D. you would have met John
If + 主语+ should +原形动词 主语+would,should,could,might或were+不定式+原形动词
If he were to come tomorrow, things would be easier.
If the sand should be broken up, it would give out much energy.
If he make the design, he might do it in some other way.
If the sea ____ to rise 50 feet, India would become an island.
A. will B. is C. was D. were
If you ____ to see Mary, what would you tell her?
A. are B. will be going C. must D. were
We might still catch the train if we ___.
A. make hurry B. haste
C. make haste D. hastily
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。
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。
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
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.
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
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。
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。
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