题目内容：

After______ ,he realized that he was wrong in doing that .
A.sometimes B.some time C.sometime D.some times
I,_______ your good friend ,will try my best to help you out .
A.who ,is B.which ,is C.that ,is D.who ,am
Who can think of a situation ________this word can be used
A.which B.that C.where D.in that
第三题为什么不能选D，在语法上有什么错误吗？