The over-speed trip device installed in some diesel engines is automatically actuated by（）

A.maintaining a constant rack setting
B.storing kinetic energy
C.maintaining equal exhaust pressure
D.maintaining even camshaft speed

A.After every trip
B.Every 4000 hours
C.According to manufacturer’s instructions
D.Every time they are shutdown

A.prevent excessive cylinder liner wear
B.reduce friction losses in the engine
C.seal the space between the piston and the liner
D.limit upward flow of lube oil into the combustion space