It was as if she were dead这里的were 为什么不用was

Susan is walking slowly as if she were tired问:为什么用were而不用was She behaves as if she were a child.为何用were而不用was? as if it 后应是were还是was? 为什么If only I were abird.中的were不用was 为什么 if i were a boy 中的were 不用was? as if it were中为什么不是as if it was? It seems as if he were an expert 为什么谓语动词要用were 而不是was If she were not so lazy ,she would pass the exam.为什么不用was? If I were a bird的英语语法问题?为什么用were 不用was? it seems as if she _ in a dream A.was B.were 虚拟语气she treats him as if he were a stranger.为什么要用were而不是用was If there_no water为什么填were 不用was