I can't understand _____.A.what does Christmas mean B.what Christmas does meanC.what mean Christmas does D.what Christmas means

I can't understand _____.A.what does Christmas mean B.what Christmas does meanC.what mean Christmas does D.what Christmas means
I can't understand _____.
A.what does Christmas mean B.what Christmas does mean
C.what mean Christmas does D.what Christmas means

I can't understand _____.A.what does Christmas mean B.what Christmas does meanC.what mean Christmas does D.what Christmas means
D
宾语从句,要用陈述句语序