一般现在时：shall/will + 动词原形
If he comes, he will bring his violin.
The volleyball match will be put off if it ___.
A. will rain B. rains C. rained D. is rained
1） 在真实条件句中，主句不能用be going to表示将来，该用shall, will.
(错) If you leave now, you are never going to regret it.
(对) If you leave now, you will never regret it.
2） 表示真理时，主句谓语动词便不用shall (will) +动词原形，而直接用一般现在时的动词形式。
If they were here, they would help you.
If she had worked harder, she would have succeeded.
The rice would not have been burnt if you had been more careful.
If my lawyer had been here last Saturday, he would have prevented me from going.
If he had come yesterday, I should / would have told him about it.
含义：He did not come yesterday, so I did not tell him about it.
If he had not been ill and missed many classes, he would have made greater progress.
含义： He was ill and missed many lessons, so he did not make greater progress.
If you succeeded, everything would be all right.
If you should succeed, everything would be all right.
If you were to succeed, everything would be all right.
If you had asked him yesterday, you would know what to do now.
If it had rained last night (过去), it would be very cold today (现在).
Were they here now, they could help us.
=If they were here now, they could help us.
Had you come earlier, you would have met him
=If you had come earlier, you would have met him.
Should it rain, the crops would be saved.
=Were it to rain, the crops would be saved.
If I were you, I would go to look for him.
If he were here, everything would be all right.
_____ to do the work, I should do it some other day.
A. If were I B. I were C. Were I D. Was I
答案C. 在虚拟条件状语中如果有were, should, had这三个词，通常将if省略，主语提前, 变成 were、should、had+主语的形式。但要注意，在虚拟条件状语从句中，省略连词的倒装形式的句首不能用动词的缩略形式。如我们可说 Were I not to do，而不能说 Weren't I to do.