高压断路器液压操作机构应具有防止（）的性能，并设置低液压（）装置。
参考答案：失压慢分、闭锁
将1～7这七个数字，分别填入下面空格内，使等式成立．（每个数字只能用一次）
口×口=口÷口=口+口-口
______×______=______÷______=______+______-______．
Little Tom _____ finished his homework; otherwise, he wouldn't be listening to music.[ ]
A. can have
B. must have
C. should have
D. might have
