they could not do anything because they did not know 《》with

they could not do anything because they did not know 《》with him A.what was wrongB.what wrong is
把wrong换成matter还是选A吗?
搞错 了 B是what wrong was

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
再问： they could not do anything because they did not know what the matter with him was呢?把was 放到后面不对吗
再答： 可以呀，可以是what the matter with him was。有时候为了保持句子的平衡，会将修饰部分后置。