介绍:
现在完成时表示过去发生或已经完成的动作对现在造成的影响或结果，也可表示过去已经开始，一直延续到现在的动作或状态。学习现在完成时，先从结构和句式开始：
1. 影响性
I have lost my pen. 我把钢笔丢了。
“丢钢笔”这个动作发生在过去，同时也在过去已经完成，但这个过过去发生和完成的动作对现在有影响——我现在无钢笔用，或我得去买支新的。
We have finished the work. 我们已把工作干完了。
显然“完成工作”这个动作发生在过去，同时也在过去已经完成，但这个过过去发生和完成的动作对现在有影响——我们可以休息了，或可以回家了，或可以做别的事了。
2. 持续性I’ve waited a week for your answer. 等你的答复我已等了一个星期。
根据句意可知，“等”这个动作发生在过去，但它在过去并没有完成，而是一直等到现在，已持续了一个星期。
构成：
主语 + have / has + 过去分词 + 其他 不规则动词需要特殊记忆
否定式：主语 + haven’t / hasn’t + 过去分词 + 其他
疑问式：Have / Has + 主语 + 过去分词 + 其他
简略答语：
Yes, 主语 + have / has.(肯定)
No, 主语 + haven’t / hasn’t.(否定)
M: Hi, Jenny! How do you like the university?
F: Hello, Bob! I like it very much.
M: Have you started your classes yet?
F: I have been to two lectures, chemistry and history.
M: Well, how were they?
F: They were very large. I&`&m not used to 300 students in class.
M: My lectures have been large too.
F: Have you been to your English class yet?
M: Yes. It was quite small. There were only about 20 students in it.
F: My classes are so far apart. The campus is sure big.
M: It sure is. My morning classes are in different buildings. I have to run between them.
Otherwise I&`&ll be late.
Have/has been 强调一个持续状态,来表示从过去到现在一直不变的情况“一直...”
The campus has been noisy. 校园里一直很吵
The students have been enthusiastic. 学生们一直很热情
Has Bob been lazy?
No, Bob hasn&`&t been lazy./ yes,Bob has been lazy./yes, he has. / no ,he hasn’t.
Has the library been crowded?
No, the library hasn&`&t been crowded.
YET 和 ALREADY,完成时态的两个标志性单词
Yet用在否定句和疑问句当中，already用在肯定句当中
Have Bob and Jenny moved into the dormitory yet?
Yes, they have moved into the dormitory already. / no, they haven’t moved into the dormitory yet.
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