四六级常考语法点预览：
一、虚拟语气
基本规则：
条件从句
主句
与现在事实相反
动词过去式
should/would+动词原形
与过去事实相反
had+过去分词
should/ would +have+过去分词
与将来事实可能相反
动词过去式/were to/should
should/ would +动词原形
与现在事实相反：
If I wereyou , I would apply forthe job.
与过去事实相反：
If I had taken your advice, I wouldn’t have made such mistake.
与将来事实相反：
If itrained tomorrow, I wouldstay at home.