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單項(xiàng)選擇題

Before welding can be done in a tank that has carried petroleum products, a certificate must be obtained from（）.

A.the customs
B.the register bureau of shipping
C.the shipyard fire department
D.a certified gas chemist

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Between the side frames on a vessel, support for the deck beams is provided by（）.

A.stanchion
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C.web frames
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單項(xiàng)選擇題

Bilge keels are fitted on ship to（）.

A.assist in drydock alignment
B.improve the vessel's stability
C.protect the vessel from slamming against piers
D.reduce the rolling of the vessel

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