现在完成时

构成：主语+助动词have, has+过去分词

用法：
1）表示过去发生的和现在有某种联系的动作，常和just, usually, already, since等时间副词连用。
　　I have just had lunch. （饱了，不用再吃了。）
　　He has had a cup of tea.（不渴了，不用再喝。）
　　They have already had their holiday. （不能再度假了。）
　　The boy has already read the book. （已经知道书的内容了，不用再看了。）

2）询问别人是否做过某事一般用现在完成时：
　　Have you finished your homework?
　　Have you been to Beijing?
　　Have he seen the film?

3）表示开始于过去并持续到现在的动作
　　I have lived in Beijing for twenty years.
　　I have worked for this school for 1 year.
4）表示一种经历，经验：去过…地方，做过…事情，经历过…事情
　　I have never had a bath.
　　I have never seen a film.
　　I have never been to cinema.
　　I have ever been to Paris.
　　Have been to表示去过，have gone to 表示去了
　　I have been to London.（人已经回来）
　　He has gone to London.（人还在那里）

5）表示一种结果，一般不和时间副词联用
　　I have lost my pen.
　　I have hurt myself.
　　He has become a teacher.
　　She has broken my heart.

句型变化：
★变疑问句将助动词移到句首，变否定句在助动词后面加not.
　　Have you lost your pen? I have not lost my pen.

★肯定回答及否定回答
　　Yes, I have. / No, I have not.

★特殊疑问句
　　What have you done?
　　What has he done?

一般过去时与现在完成时的区别：
　　凡是有明确的表示过去的时间状语的句子为过去时。
　　注意：有些动词表示的动作有一个终点，不能再延续，因此不能和表示一段时间状语连用。
　　错：I’ve left Beijing for 3 days.
　　对：I left Beijing 3 days ago. I have been away from being for 3 days.