—Pandas are very beautiful, _______ kind of shy. Do you think so?         

—Sure. And they are the treasure of our country.      [ ]

A. and        

B. so            

C. but      

D. or

长期停用的计算机控制系统，需每月通电进行相关检查和试验，确保计算机控制系统处于完好状态。