在完成时由“助动词have (has)+动词的过去分词”构成
表示发生在过去的对现在仍有影响的动作时,时间状语有:already, yet, just, once, twice,ever, never,three times, before等
I have never seen such fine pictures before. (我以前从来没有看过这么好的画)
表示在过去开始一直延续到现在(可能延续下去)的动作或状态时,时间状语有:for (two years),since 1990, since (two weeks ago)和since引导的状语从句
I have been away from my hometown for thirty years.(我离开家乡有30年了)
have been to与have gone to的区别:have gone to(“已经去了”)表示人不在这里,have been to(“去过”)表示人在这里
-Where is Mr Li?
–He has gone to the UK.
(李先生在哪里?他去了英国。)
-Do you know something about Beijing?
–Yes,I have been to Beijing three times.
(你知道北京的情况吗?是的,我去过那里三次。)
在完成时中,一个瞬间性动词(一次性动作)不能与表示一段时间的状语连用,此时须将该瞬间动词改为延续性动词或状态动词
It is / has been + (多久)+ since + 主语(人)+谓语(过去时)+……+过去时间状语
注意:在其它的时态中也存在类似问题,关键是:瞬间动词不能和表达一段时间的状语连用
How long may I keep the book?
(这本书我能借多久?)(句子中keep取代了borrow)