母线的构架、绝缘子底座应接地良好，无松动断裂现象。
参考答案：对
Tom _____ have come in person. He came such a long way just to tell us the result. [ ]
A. mustn't
B. needn't
C. wouldn't
D. couldn't
旋塞材质不好造成水位表旋塞泄漏故障时，应（）
A、关闭旋塞
B、更换填料
C、更换旋塞
D、更换玻璃管
