单项选择题
The piston cooling system may employ similar components, except that （） is used instead of a head tank.
A.a sump tank B.a feed well C.a double bottom tank D.a drain tank
单项选择题 The pistons are cooled by oil supplied from the forced （） system.
单项选择题 The period when both inlet valves and exhaust valves are open is referred to as （）.
单项选择题 The period of valve overlap is when （）.
