单项选择题
The self-contained breathing device should not be used in which situation?（）
A.Oxygen deficient spaces
B.Compartments containing poisonous vapors
C.Fighting fires that produce heavy smoke
D.Underwater search
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A.weigh down the anchor
B.lubricate the anchor
C.repel dangerous fish
D.smooth the sea -
单项选择题
The process of waiting a period of time before pretensioning an anchor is known as（）.
A.soaking
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C.sinking
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The most probable position of the object of a search at any given time is the（）.
A.datum
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