一、什么是现在完成时？

现在完成时是一种重要的英语时态，主要用于描述过去发生的动作或事件对现在产生的影响，或者表示从过去某一时间开始并持续到现在的状态或活动。其结构通常为“have/has+过去分词”。

二、专项练习题

1. 单项选择题

(1) I ________ my homework already.

A. finish B. finishes C. have finished D. am finishing

(2) She ________ the book twice.

A. read B. reads C. has read D. is reading

(3) They ________ to the park every weekend.

A. go B. went C. have gone D. have been going

(4) He ________ a new job last month.

A. finds B. found C. has found D. had found

2. 句型转换

(1) I have cleaned the room. (改为否定句)

I ________ cleaned the room yet.

(2) She has lived here for five years. (就划线部分提问)

________ ________ has she lived here?

3. 翻译句子

(1) 我已经吃过了早饭。（翻译成英文）

I ________ ________ breakfast.

(2) 他已经完成了作业。（翻译成英文）

He ________ ________ his homework.

三、答案解析

单项选择题答案：

(1) C (2) C (3) D (4) B

句型转换答案：

(1) haven't (2) How long

翻译句子答案：

(1) have had (2) has finished

四、总结

通过以上练习，我们可以更好地掌握现在完成时的基本用法和结构。希望同学们能够灵活运用这些知识，在实际交流中更加得心应手！如果还有疑问，可以随时查阅相关语法书籍或向老师请教。

---

（注：本文内容为原创，旨在帮助学生巩固英语语法知识，提高语言能力。）