习惯表达是what's wrong with sb.(something is wrong with sb.)
what 是对主语提问的,应该是what +正常语序,所以在宾语从句中,不需要再改变语序.同时又是过去式,因此答案为A.
如果将wrong 改成the matter ,答案就不是A了,因为what's the matter是对表语提问,the matter 是主语,是what +一般疑问句,如果整句做宾语(从句),应该是know what the matter is/was.
所以正确的句型是:
1.they could not do anything because they did not know what was wrong with him
2.they could not do anything because they did not know what the matter was with him