柱上断路器是一种担负（）任务的开关设备。
A、控制
B、保护
C、控制和保护
D、过负载
参考答案：C
The first-round English revision ______ in Senior Grade Three of the No.2 High School of Baoding. [ ]
A. is being done
B. is doing
C. have done
D. had been done.
波士顿(BCG)矩阵中现金牛业务的特点是( )。
A．高增长，低市场份额
B．高增长，高市场份额
C．低增长，高市场份额
D．低增长，低市场份额
