问题
The students were____ over the____ problem,listening to the teacher with a ____ expression on theirfaces.[ ]
A: puzzled; puzzling; puzzling
B: puzzled; puzzling; puzzled
C: puzzling; puzzling; puzzled
D: puzzling; puzzled; puzzling
B: puzzled; puzzling; puzzled
C: puzzling; puzzling; puzzled
D: puzzling; puzzled; puzzling
正确答案是：
