句子1 were it not .使用的是虚拟语气 条件句的倒装现象 这种情况因为省略了if 主句部分是与现在的现实相反
If从句中若含有should,had 或者were,那么就可以把它们放在句首,与主语颠倒形成倒装,但动词过去式不可以与主语倒装.
如果他在,他会来帮助我们.Were he here,he would come to help us.
假如你刚才在这里,你就会遇见她.Had you been here just now,you would have met her.
假如我明天看见他,我就会告诉他关于这一切.Should I see him tomorrow,I would tell him about it.
主句部分表达过去的事情对现在的影响.我觉得不能用would never been 要用would never have been what
句子2 当条件状语从句表示的行为和主句表示的行为所发生的时间不一致时,被称为“错综时间条件句”,动词的形式要根据它所表示的时间作出相应的调整.
假如我不忙,我就会来了.If I were not busy,I would have come.
句子3 与将来事实相反 从句的谓语用If I (we,you,he,they) ＋动词过去式或 were to do 或should do 形式,主句谓语用should（第一人称）/would（第二、三人称）/could/ might ＋动词原形.
假如他来了,我们对他说什么呢?If he were to come,what should we say to him.