单项选择题
A.correct maneuvering
B.wear
C.working efficiency
D.maintenance
单项选择题 The way to reduce （） is to build up a film of lubricant between any two surfaces that rub against each other.
单项选择题 The viscosity regulator controls the fuel oil temperature （） provide oil at the correct viscosity for combustion.
单项选择题 The viscosity regulator controls the （） of the fuel oil in order to provide the oil at the correct viscosity for combustion.