是用 were
虚拟语气在条件句中的用法：
1.与现在事实相反
主句时态：Shouldwouldcouldmight+do（动词原形）
从句时态：过去式（be动词各人称都用were）
例句：If I were you,I should would make full use of my time to study.
2.与过去事实相反
主句时态：Shouldwouldcouldmight+have done（动词过去分词）
从句时态：Had+done(过去分词)
例句：If you had come earlier,you would have met him.
3.与将来事实相反
主句时态：Shouldwouldcouldmight+do（动词原形）
从句时态：（可以使用下列其中之一时态）
a.过去式（be动词各人称都用were）
b.should+动词原形
c.were to +动词原形
例句：If it rained should rainwere to rain tomorrow,the crops would be saved.