Which one is not the normal operation for boiler shutdown?（）
A. Carry out soot blowing if permissible
B. Change fuel supply to diesel oil
Close steam stop valves on boiler when pressure is reduced
Drain boiler empty when it has cooled dow
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接续金具的作用是用于（）的接续和修补。
A. 导线和绝缘子
B. 绝缘子与绝缘子
C. 避雷线和导线
D. 绝缘子与杆塔
You can safely step in the bight of a line（）.
A. when it is not under strain
B. if both ends are made fast
C. in an emergency
D. at no time
城市轨道交通系统中直线轨距标准为（）
A. 1435mm
B. 1353mm
C. 1433mm
D. 1432mm
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