回答如下：

who引导的宾语从句在从句中可以作主语、宾语、表语。例如：

1、 I don't know who broke the vase. 

2、 We cannot tell who he is. 

3、 We know who he is waiting for. 

4、 Do you know who she likes? 

5、 I know who she wants to have go there.