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單項(xiàng)選擇題

For any piston ring to operate smoothly without scuffing ,the ring must be （）.

A.of a material harder than the cylinder liner
B.properly lubricated
C.prevented from compressing
D.prevented from rotating during engine operation

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單項(xiàng)選擇題

Shaker, circulation and spray are the three general methods used in（）

A.pre-injection fuel oil treatment
B.lube oil filtration
C.lube oil purification
D.piston cooling

單項(xiàng)選擇題

Wristpin bearings are difficult to lubricate because of their oscillating motion and（）

A.their free-floating design
B.their relatively small size
C.the reciprocating motion of the piston
D.their position in the lubrication system