43.
(A) whether
(B) what
(C) that
(D) which

what 用法

what = 先行詞+關係代名詞

what = the thing which

= that which

= all that

請把以下”先行詞+關係代名詞”改成what

因為使用what句子變簡短有力了。

 This is the thing which I need. = ? This is what I need.

Do you understand all that I said? = ? Do you understand what I said?

He saves all that he earned. = ? He saves what he earned.

The thing which he said is true. = ? What he said is true.

注意:

因為what本身已經有先行詞和關係代名詞的意義了，所以如果出現what，前面就不應該再出現先行詞，例如: that, the thing,…

what 本身就可以當作主詞、受詞或補語，(和which, that不同，which, that 只能當關係代名詞使用)

來源：

http://bearwithprim.pixnet.net/blog/post/312118271-%E9%AB%98%E4%B8%AD%E8%8B%B1%E6%96%87%3Awhich-that-what%E9%97%9C%E4%BF%82%E4%BB%A3%E5%90%8D%E8%A9%9E

【音樂文法教室】3首歌3個步驟，讓你搞懂「關係代名詞」的用法 – 初級篇