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（）

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

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℃