题目内容：

they want to know ___do help us a.how they can b.what they can 选哪个

优质解答

b.what they can
they want to know (what they can do)
括号内是宾语从句.
(to)help us 这是省略了to的不定式.
他们想知道,他们能做些什么,来帮助我们.