2017年6月英语四级语法知识点:主动形式
过去 现在 将来 过去将来
一般
did do will/shall do should/would do
进行
was/were doing am/is/are doing will/shall be doing
完成
had done have/has done will/shall have done should/would have done (用于虚拟语气)
完成进行
had been doing have/has been doing /