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.那决不能用was了吧是的，不能用was，不管主语是什么，只要是be动词，都要用were。