问题补充：
The math problem is so hard. I really don’t know.
A. how to do it
B. how to do
C. what to do it
D. where to do it
答案：
(答案→)A. how to do it
B. how to do
C. what to do it
D. where to do it
解析：how如何，怎样；what什么；where在哪儿。句意：这道数学题是这么难。我真的不知道如何解答。选项B缺少逻辑宾语，结合语境可知选A。
