In fact he had done ____ he could to help the poor.

In fact he had done ____ he could to help the poor.
A、what
B、which
C、as
D、all which
【正确答案】：A
【题目解析】：本题测试宾语从句的用法。what引导宾语从句， what在从句中做宾语。本句的意思是；“事实上，他在尽一切所能帮助穷人。”