单项选择题
The rim of the piston may contain cut-out portions to accommodate （） when they open.
A.the gases B.the air C.the valves D.the injectors
单项选择题 The removal of （） from lubricating oil will reduce engine wear and possible breakdowns.
单项选择题 The remaining oil in the lubricating pipes and ducts should be blown out with （）.
单项选择题 The quantity of oil injected into the cylinder can be regulated （）.
