--- Did you ask the guard happened?
--- Yes, he told me all he knew.
A. what; that
B. what; what
C. which; which
D. that; that
网友回答
(答案→)A. what; that
B. what; what
C. which; which
D. that; that
解析：what happened是宾语从句. all 之后that he knew是定语从句.先行词是all,所以关系代词只能用that.