单项选择题

（） is not usually used in liquid cargo systems.

A.Hydraulic drive systems
B.Electric drive systems
C.Steam drive systems
D.Man-powered drive systems

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单项选择题
（） is not one of the winch controls.

A.a master controller or switchbox
B.a group of relays
C.contactors
D.a solenoid brake
单项选择题
When checking the oxygen content of the cargo tanks prior to loading cargoes requiring vapor recovery，the atmosphere must be sampled（）.

A.one meter from the tank bottom and one meter below the tank top
B.one half the ullage of the tank and one meter below the tank top
C.one half the ullage of the tank and one meter above the tank bottom
D.at three meter intervals from the tank top
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