是用 were
虛擬語氣在條件句中的用法：
1.與現(xiàn)在事實相反
主句時態(tài)：Should\would\could\might+do（動詞原形）
從句時態(tài)：過去式（be動詞各人稱都用were）
例句：If I were you,I should \would make full use of my time to study.
2.與過去事實相反
主句時態(tài)：Should\would\could\might+have done（動詞過去分詞）
從句時態(tài)：Had+done(過去分詞)
例句：If you had come earlier,you would have met him.
3.與將來事實相反
主句時態(tài)：Should\would\could\might+do（動詞原形）
從句時態(tài)：（可以使用下列其中之一時態(tài)）
a.過去式（be動詞各人稱都用were）
b.should+動詞原形
c.were to +動詞原形
例句：If it rained \should rain\were to rain tomorrow,the crops would be saved.