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。