- 搜標(biāo)題
- 搜題干
- 搜選項(xiàng)
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
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