The doctor （ ） is treating for your heart trouble is a friend of mine.
（A）who
（B）when
（C）which
（D）whom
The book （ ） isn't in the library. 选项：
（A）what I need
（B）I need
（C）that I need it
（D）which I need it
It was raining, （ ） was a pity. 选项：
（A）what
（B）which
（C）that
（D）it
