虚拟条件句的从句部分如果含有were, should, 或had, 可将if省略，再把were, should或had 移到从句句首，实行倒装。

上海新东方夏令营，介绍
　 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.

注意：
　 在虚拟语气的从句中，动词'be'的过去时态一律用"were"，不用was， 即在从句中be用were代替。
　 if i were you, i would go to look for him.
　　 如果我是你，就会去找他。
　 if he were here, everything would be all right.
　　 如果他在这儿，一切都会好的。