试从国际关系理论的角度分析两大军事集团形成的原因。
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雷雨季节，管线维护人员巡线检查时，应远离发生雷电的地区，避免（）。
化工装置上常使用到一种阀门叫疏水阀，它起到什么作用？
When is the density of the water required to be logged in the logbook of a ship?（）
Any time the vessel moves from water of one density into waters of a different density
B. Prior to getting underway when the vessel is floating in fresh or brackish water
C. Only when the vessel moves from fresh water into salt water
D. The density of the water is not required to be logged in the unofficial logbook
起重机正在吊物时，任何人不准在吊杆和吊物下停留或行走。
A. 正确
B. 错误
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