问题补充：
They want to know do to help us.
A. what can they
B. what they can
C. how they can
D. how can they
答案：
A. what can they
(答案→)B. what they can
C. how they can
D. how can they
解析：首先要选择间接引语部分是陈述词序的选项；第二要考虑疑问词的正确使用，从句子结构来看，间接引语部分的谓语do缺少了宾语，因此应选择连接词what充当do的宾语。
