基本养老金由哪几部分组成？

A. 菱形结构
B. 梯形结构
C. 正金字塔结构
D. 倒金字塔结构

A. prevent excessive cylinder liner wear
B. reduce friction losses in the engine
C. seal the space between the piston and the liner
D. limit upward flow of lube oil into the combustion space

A. 正确
B. 错误