第四章 完成式（perfect tense）
4-2现在完成进行式（present perfect progressive tense）
在上一节，我们知道，如果有一个行动，从过去发生后，就一直延续到现在，我们可以用现在完成式。举例来说，以下的例子都应该用现在完成式：
（1）自从1974年，我就在学校学英文。
since 1974, i have studied english at school.
（2）自从我大学毕业以后，我就在这里工作。
since i graduated from college, i have worked here.
以第一句话为例，假如我们要强调我一直在练习游泳，而且没有间断，我们可以用现在完成进行式（present perfect progressive tense）。
所谓现在完成进行式，形式：verb to have + been + present participle
verb to have 是为了完成式，been 和 present participle 都是为了进行式。
以下是现在完成进行式的例子：
i have been studying english since 1974.
i have been working here since i graduated from college.
i have been living here since i was a child.
he has been acting like a fool lately.（他最近一直在做傻事）
they have been dancing since seven o’clock.
it has been snowing since yesterday.
i have been taking music lessons since last year.
he has been drinking heavily since last year.（他去年起，就一直在酗酒）