单项选择题
A.by an fuel valve
B.through an inlet valve
C.with an exhaust valve
D.from an outlet valve
单项选择题 In the sentence “In some designs the cylinder oil is timed so that the oil injects only on the piston ring belt, the "piston ring belt" means （）.
单项选择题 In the four-stroke engine, it takes （） to make one power stroke.
单项选择题 In the event of the cylinder starting valve leakage （） would pass into the air pipes and ignite the oil deposited.