He said he was busy, which was true.

他说他很忙，这是真的。

　　在这个句子中，关系代词which代表整个主句的意思；在从句中，又充当主语的成分。
　　例句：
　　Watt watched a steaming kettle for quite a while, which rather annoyed his aunt.
　　瓦特看那个冒气的水壶看了好长一段时间，这使他的姑妈非常恼火。
　　The Foreign Office is still holding up my passport, which worries me much.
　　外交部仍然压着我护照，这让我很担心。