煤电钻必须使用设有检漏、____、短路、过负荷、断相、远距离起动和停止煤电钻功能的综合保护装置。____必须对煤电钻综合保护装置进行一次跳闸试验。
参考答案:漏电闭锁、每班使用前
巧算.
(1)12.5×3.9×8
(2)4.3×2.5×0.4
(3)0.125×6.4
(4)36×0.25.
— Is Jack on duty today?
— It ____ be him; it's his turn tomorrow. [ ]
A. must's
B. won't
C. can't
D. needn't