宾语从句应该用陈述语序.
eg: I asked him how old he was.
I don't know what his name is.
其实What is the matter?和What is wrong?本身都是陈述语序,所以在宾语从句中语序都不用变化.可以说Mum asked me what was the matter.或Mum asked me what was wrong.
所以严格说来,这个题应该没有正确答案.
如果从出题意图来看,这个题不只考察语序,还考察了时态,根据时态（过去时）排除AB,在CD中,D项是肯定不对的,因为what is wrong本身是主系表陈述语序（没有别的理解方法,因为wrong是形容词,不能作主语）,宾语从句也要说成what was wrong.而C项中用到了what is the matter的陈述语序,what is the matter?译为“怎么了?”时,规定它就是陈述语序（也就是what是主语,is是系动词,the matter是表语）,但从形式上看,也可以说the matter是主语,is是系动词,what是表语,那么它的陈述语序就成了what the matter is,所以就有了答案C.