单项选择题
A.the solid impurities of large particle
B.the solid impurities of fine particle
C.the water content
D.both water and solid impurities
单项选择题 Impurities in the fuel oil will affect the operation of the engine, which has （） the use of separator and some other devices.
单项选择题 The lube oil to lubricate the surfaces of the cylinder liners is spread over by the （）.
单项选择题 The most important factor that causes the wear of the engine parts is （）.