大学英语四级语法精要：非谓语动词的完成进行式
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非谓语动词的完成进行式: 在谓语所表示的时间之前一直进行的动作, 就要用不定式的完成进行式.
The struggle was known to have been going for twenty years.
We are happy to have been working with you.
The struggle was known to have been going for twenty years.
We are happy to have been working with you.