The students were over the problem listening to the teacher with a expression on their

问题补充：

The students were over the problem，listening to the teacher with a expression on their faces.

A. puzzled；puzzling；puzzling

B. puzzled；puzzling；puzzled

C. puzzling；puzzling；puzzled

D. puzzling；puzzled；puzzling

答案：

A. puzzled；puzzling；puzzling

(答案→)B. puzzled；puzzling；puzzled

C. puzzling；puzzling；puzzled

D. puzzling；puzzled；puzzling

解析：形容词辨析。Puzzled感到困惑的,通常形容人；puzzling令人困惑的，通常形容事物；expression表情，它与人有关，所以仍然用puzzled修饰。句意：带着困惑的表情听老师讲课，学生们对于那个令人困惑的问题感觉很困惑。