Question

---       unusual music he is playing! 

--- Yes, all of the students are losing themselves in it.

1. A.
   How
2. B.
   What an
3. C.
   How a
4. D.
   What

Answer 1

D
将后文主谓即he is playing去掉之后，最后一词为music是音乐，为不可数名词故选D