2015年卫生职称英语语法之现在完成时：

1.形式：

1）现在完成时由助动词have（has）+过去分词构成。除第三人称单数用has外，其他人称一律用have.

2）过去分词的形式有规则的和不规则的两种。前者由动词原形+（e）d构成，如worked，used，studied，stopped等，后者如made，gone，written，cut等，须逐个记忆。

2.基本用法：

1）用于表示动作现在已经完成：

e.g. We have just come back.

e.g. She has written three books up to now.

2）表示过去发生但对现在有影响的动作。可以不用时间状语，但也可和一些不确定过去时间的副词连用，如already，before，ever，never，just，once，recently ，yet等，例如：

e.g. Who has broken the window?谁把窗户玻璃打破了？

e.g. We have never seen such a film before.我们以前从没有看过这样的一部电影。

3）也可表示过去某时开始的动作一直延续到现在，而且可能继续延续下去，常和for引导的短语或和since引导的短语或从句连用。

e.g. We have studied English for more than 10 years.

e.g. He has lived here since he divorced Mary.

3.完成时态的否定结构

e.g. We have seen such a film before. - We haven't seen such a film before./We have never seen such a film before. /We have rarely/hardly seen such a film before.