虚拟语气中为什么用were

Question

Mary loves the baby so much as if she were his mother.
这其中were为什么不改成was？

Answer 1

这是虚拟语气的固定用法。虚拟语气对现在的虚拟有两种，【实意动词用过去式，be动词用were（不能用was）】。这两种分别举例如下：
If he finished his homework， I would be so surprised。 如果他现在完成了作业，我会很吃惊的。
If I were you ， i would go to the cinema。 如果我是你，我就去电影院。追问

那决不能用was了吧

追答

是的，不能用was，不管主语是什么，只要是be动词，都要用were。