单项选择题

Oil product samples should be taken from the（）.

A.dock riser
B.ship's cargo tanks
C.shore tank discharge
D.All of the above

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单项选择题

For any given pedestal crane，when the boom is lengthened，the lifting capacity is（）.

A.unchanged
B.increased
C.eliminated
D.decreased

单项选择题

For a given weight of cargo，the stress on the heel block of a cargo boom（）.

A.increases as the cargo closes the head while hoisting
B.increases if the cargo runner is doubled up
C.decreases as the boom is topped to a greater angle
D.is determined by the thrust stresses on the boom