发动机润滑系具有四大作用，其中（）作用主要是靠润滑油循环流动来实现的。
参考答案：清洁冷却
With the development of modern society, some traditional customs are gradually . [ ]
A. dying of
B. dying out
C. dying down
D. dying off
The proverb "Pride goes before a fall." is derived from ______.
A. Christianity B. the BibleC. Greco-Roman Civilization D. geographic knowledge
