CENTUM CS系统总貌窗口中显示稳定灰色的含义是（）。
A.通信误差
B.通信显示块
C.新产生的报警正在等待确认
D.报警状态已被确认
参考答案：A
The major goal of USB was to define an external expansion bus which makes adding (71) to a PC as easy as hooking up a telephone to a wall-jack. USB 2.0 is an evolution of the USB 1.1 (72) , providing a higher performance interface.
A．protocol
B．specification
C．prescript
D．rule
虚函数必须是类的 【12】 。
