当采用计算机（）系统时，就地开关柜上应保留必要的测量表计或监测单元
A.监测
B.监控
C.自动化
D.综合自动化
参考答案：B
_______the safety of gas, the government has checked the city's gas supply system thoroughly. [ ]
A. To ensure
B. Ensuring
C. Having ensured.
D. To have ensured
已知a，b，c成等比数列，a，m，b和b，n，c分别成两个等差数列，则＋等于 ( )
A．4
B．3
C．2
D．1
