单项选择题

Cooling enables the engine metals （） their mechanical properties.

A.to retain
B.to remain
C.to maintenance
D.to have

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单项选择题

A.good lubrication
B.low thermal stress
C.good mechanical properties
D.acid corrosion

单项选择题

A.for starting diesel engines
B.in pneumatic control system
C.in pneumatic tools
D.All the above are true

单项选择题

A.the air receivers
B.the starting valves
C.the cylinder covers
D.the distributors