if的用法，虚拟语气as

as if从句的虚拟语气也是按照谓语动词发生的时间来体现: 指现在用动词的过去式(be 一般用were，口语可用was)，指过去用动词的过去完成式had +过去分词，指将来一般多用would也可用could+动词原形。例如It looks as if it were going to rain.看起来好像要下雨。