代理服务器是工作在哪种模式下的？（）
A、B/S
B、C/S
C、S/C
D、S/B
参考答案：C
— Is there _____ in the box?
— No, _____. [ ]
A. something; anything
B. anything; something
C. anything; nothing
D. nothing; anything
什么是环境？如何分类？
