选A.
这是一句宾语从句,从句要保持陈述句语序.但问题是,What's the matter with him?的主语就是What,the matter with him 是表语.所以该问句的语序和陈述句语序一致.不用再调整.
举例说明：
He's my father.陈述句
Who's my father?疑问句,疑问词作主语,所以仍属陈述句语序.
Do you know who's my father?
Who's he?主语为he
Do you know who he is?
总结：
what's the matter with...,what's wrong with...,which is the way to...等都属系表结构,疑问词就是主语,作宾语从句时,都不必调整语序.