题目内容：

His math is poor,you must ________ him.A.try help B.trying to help C.try to help

优质解答

C.
他的数学不好,你一定要尽力帮助他
must是情态动词,情态动词后用动词的原型所以删除B
try to do sth.是尽力做某事的意思,.