2015年衛(wèi)生職稱英語語法之現(xiàn)在完成時：

1.形式：

1）現(xiàn)在完成時由助動詞have（has）+過去分詞構(gòu)成。除第三人稱單數(shù)用has外，其他人稱一律用have.

2）過去分詞的形式有規(guī)則的和不規(guī)則的兩種。前者由動詞原形+（e）d構(gòu)成，如worked，used，studied，stopped等，后者如made，gone，written，cut等，須逐個記憶。

2.基本用法：

1）用于表示動作現(xiàn)在已經(jīng)完成：

e.g. We have just come back.

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

2）表示過去發(fā)生但對現(xiàn)在有影響的動作。可以不用時間狀語，但也可和一些不確定過去時間的副詞連用，如already，before，ever，never，just，once，recently ，yet等，例如：

e.g. Who has broken the window?誰把窗戶玻璃打破了？

e.g. We have never seen such a film before.我們以前從沒有看過這樣的一部電影。

3）也可表示過去某時開始的動作一直延續(xù)到現(xiàn)在，而且可能繼續(xù)延續(xù)下去，常和for引導的短語或和since引導的短語或從句連用。

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

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

3.完成時態(tài)的否定結(jié)構(gòu)

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.