（） is the removal of exhaust gases by blowing in fresh air.

（） is sometimes used for piston cooling since leaks into the crankcase would not cause problems.

A.Diesel oil
B.Hydraulic oil
C.Lube oil
D.Mineral oil

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（） fuel oils （） lubricating oils require treatment before passing to the engine.

A.Both；and
B.Neither；nor
C.Either；or
D.Both；or

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