普通弹簧管压力表用于不同介质时，应喷涂不同的颜色，如燃料气用（）。
A、褐色
B、红色
C、深绿色
D、白色
参考答案：B
若a，b为实数，则“2a＞2b”是“log2a＞log2b”的（ ）
A．充分非必要条件
B．必要非充分条件
C．充要条件
D．非充分非必要条件
Many of the things that_________ thought useless_________ man today.[ ]
A. used to be; used to serve
B. were used to being; are used to serving
C. were used to be; are used to serve
D. used to be; are used to serve
