单项选择题
The main function of the lubrication system in to enable （） of a film of oil between the moving parts.
A.the information B.the formation C.the scatter D.the friction
单项选择题 The main factor which determines the output of each cylinder is （）
单项选择题 The main factor determining the output of each cylinder is the cylinder （）.
单项选择题 The main bearings are provided with thin-walled （）, lined with a copper-lead alloy.
