单项选择题

If the hatch cover does not move, （）should be checked.

A. the open valve
B. the stop valve
C. the steam valve
D. the close valve

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单项选择题
To ensure the safety in operating hatch covers, oil the moving parts （）.

A. monthly
B. every three months
C. once monthly
D. every two months
单项选择题
During operation, the （）should check the working condition of the derrick.

A.foreman
B.operator
C.opener
D.stevedore
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