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單項(xiàng)選擇題

Before leaving the harbour, all derricks must be （）properly.

A.tightened
B.secured
C.unfastened
D.loaded

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單項(xiàng)選擇題

（）operation, any obstacles in the way of hatches must be removed and cleaned.

A.Before
B.During
C.After
D.Within

單項(xiàng)選擇題

Each （）consists of two or more panels.

A.cover
B.hatch
C.derrick
D.winch