For diesel engine piston cooling, lubricating oil can be supplied to the pistons by a/an （）.

A.twice the crankshaft speed
B.half the crankshaft speed
C.the same speed as that of the crankshaft
D.a speed independent of that of the crankshaft

A.failing to reach rated speed
B.knocking under maximum load
C.hunting or surging under light load
D.overspeeding and running away

A.cooling water pump
B.nozzle cooling passages
C.cylinder jackets
D.heat exchanger