I had explained everything _________ I knew to him, but he didn’t believe me．

I had explained everything _________ I knew to him, but he didn’t believe me．

A.which

B.what

C.all

D./

答案及解析： D

解析：

“我向他解释了我知道的一切事情，但是他仍然不相信我。”因为先行词everything是不定代词，只能用that引导定语从句，也可省略that。