4. 连接代词who, whom, whose, what, which, whoever, whatever, whichever
连接副词 where,
when, how, why。如:
The problem is who we can get to replace
her.
问题是我们能找到谁去替换她呢。
The question is how he did it.
问题是他是如何做此事的。
That was what she did this morning on
reaching the attic.
那就是她今晨上了阁楼干的。