He joined the League three years ago.

( 三年前入团，joined为短暂行为。)

I have finished my homework now.

---Will somebody go and get Dr. White?

---He's already been sent for.

句子中如有过去时的时间副词(如 yesterday, last, week, in 1960)时，不能使用现在完成时，要用过去时。

(错)Tom has written a letter to his parents last night.

(对)Tom wrote a letter to his parents last night.

过去完成时

1) 概念：表示过去的过去

----|-------|-----|---->其构成是had +过去分词构成。

那时以前 那时 现在

2) 用法

a. 在told, said, knew, heard, thought等动词后的宾语从句。

She said (that) she had never been to Paris.

b. 状语从句

在过去不同时间发生的两个动作中，发生在先，用过去完成时;发生在后，用一般过去时。

When the police arrived, the thieves had run away.

c. 表示意向的动词，如hope, wish, expect, think, intend, mean, suppose等，用过去完成时表示"原本…，未能…"

We had hoped that you would come, but you didn't.

3) 过去完成时的时间状语before, by, until , when, after, once, as soon as。

He said that he had learned some English before.

By the time he was twelve, Edison had began to make a living by himself.

Tom was disappointed that most of the guests had left when he arrived at the party.

现在完成进行时 :

其构成形式如下：

I / we / they have

He / she / it has been + 动词的现在分词

功用如下：

1) 表示一个在过去开始而在最近刚刚结束的行动，如：

Ann is very tired. She has been working hard.

Why are you clothes so dirty? What have you been doing?

2) 表示一个从过去开始但仍在进行的行动，如：

It has been raining for two hours. (现在还在下)

Jack hasn’t been feeling very well recently.

3) 表示一个从过去开始延续到现在，可以包括现在在内的一个阶段内，重复发生的行动，如：

She has been playing tennis since she was eight.

4) 现在完成时强调动作行为的结果、影响，而现在完成进行时只强调动作行为本身，如：

Tom’s hands are very dirty. He has been repairing the car.

The car is going again now. Tom has repaired it.

注意：

现在完成时有否定结构、而现在完成进行时没有否定结构。

现在完成时态可表示做完的时期以及已有的经验、但现在完成进行时不可以

现在完成进行时的用法就为大家讲解到这里，精品学习网希望大家可以掌握该知识点。

相关链接

高中英语语法一般过去将来时分析讲解 

高中英语语法人称代词的用法讲解