2015年卫生类职称英语考试语法：时态

1)现在完成进行时态 (have/has been + -ing 分词构成): 动作或状态从过去某时开始,继续到现在,可能继续下去,也可能刚刚结束.

I've been writing letters for an hour.

I've been sitting in the garden.

2)过去完成进行时(由had been + ing分词构成): 过去某个时刻以前一直在进行的动作

I'd been working for some time when he called.

We had been waiting for her for two hours by the time she came.

3)将来完成进行时: 将来某个时刻以前一直在进行的动作.

By next summer, he will have been working here for twenty years.

In another month's time she'll have been studying here for three years.

4)将来完成时(由shall/will have + 过去分词构成): 将来某时已发生的事.

I shall have finished this one before lunch.

They'll have hit the year's target by the end of October.