In machinery space, the valves, pipes should be（）

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

单项选择题The oil pressure and flow from each bearings can be checked when（）

A.the lubricating pumps are stopped and the access doors are opened
B.the lubricating pumps are running and the access doors are opened
C.the engine is running and the access doors are closed
D.the engine is stopped and the access doors are closed

单项选择题When preparing an engine for water temperature（）

A.should be kept at a proper level by a cooler
B.should be raised to about 80℃ by a heater
C.should be raised gradually
D.should be lowered to about 60℃

单项选择题When stand-by engine instructions have been received, it’s necessary to make it sure that all valves in the various systems are（）

A.operational
B.open
C.closed securely
D.at middle position