单项选择题
The piston ring grooves for a standard engine are （）
A.chromium-plate against wear B.anti-corrosion treated C.white metal lined against wear D.flame hardened against wear
单项选择题 The piston moving up and down keeps the crankshaft （）.
单项选择题 The piston moves up and down, thus causing the rotational movement of the（）
单项选择题 The piston cooling system may employ similar components, except that a drain tank is used instead of a head tank That means this system （）.
