单选题For any piston ring to operate smoothly without scuffing ,the ring must be （）.Aof a material harder than the cylinder linerBproperly lubricatedCprevented from compressingDprevented from rotating during engine operation
单选题
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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