单项选择题
A.piston crown
B.piston ring groove
C.piston skirt
D.piston ring area
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.
单项选择题 In the （） pressure charging system the pulse of energy that occur as the exhaust is released from the cylinder to improve the output of the turbocharger.