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

未来五年，平凉市将争取设立中国（兰州）自由贸易园区，推进国际贸易“单一窗口”建设，营造法治化、国际化、（）的营商环境。

A.市场化

B.专业化

C.便利化

D.人文化