In order to remove the carbon deposit from the threaded recess, we can use（）

单项选择题Waste oil should（）

A.be treated according to the C-Es command exactly
B.be treated according to MARPOL
C.accumulate in bilges or on tank tops in accordance with MARPOL
D.discharge to sea at the specified areas

单项选择题All items such as steam pipes, exhaust pipes and fittings which, because of their location and operating temperature, present a hazard should be adequately lagged.That means the items should（）

A.not be put into operation too early
B.be pay adequate attention to
C.be used only when necessary
D.be coated with certain material

单项选择题In machinery space, the valves, pipes should be（）

A.arranged as close to each other as possible to save space
B.arranged far away from each other for convenient operation
C.be fixed or clamped to avoid vibration
D.kept easy removable as to convenient repairing work

单项选择题The guard, fencing or shielding for moving parts or machinery can be removed for repair only when the machinery it belongs to（）

A.stays at rest
B.is working stably
C.is worn out
D.is in good operation

单项选择题Before starting an engine by air, the engine must（）

A.be turned by a turning gear for at least one minute
B.be turned by a turning gear for at least two minutes
C.be turned at least one complete turn
D.be turned at least two complete turns