电力监控系统由那几部分构成？
参考答案：电力监控系统由设置在控制中心的中央级监控系统、设置在各种变电所内的变电所级系统以及联系两者的通信通道构成。
Jack’s parents can’t go to the parents’ meeting because they ________ to Beijing on business.
A．went
B．have gone
C．will go
D．had gone
Would you like ___ football or ___ piano?[ ]
A. to play, to play
B. playing, to play the
C. to play, to play the
D. playing, playing the
