1.if he___ here this afternoon i would go with him.a.should be b.were 答案是b为什么不能选a?

题目

1.if he___ here this afternoon i would go with him.a.should be b.were 答案是b为什么不能选a?
a也是对将来的虚拟啊

答案

if引导的条件状语从句,虚拟语气的,有以下几种情况：
1、if were to do,would do
2、if +过去式,would have done
3、if had done,should have done