单项选择题
If the engine is naturally aspirated, or is a small high-speed type with a centrifugal turbocharger, the period of valve overlap（）,ie when both valves are（）, will be and the exhaust valve will close some 10°top dead canter（）.
A.open；short；after B.closed；short；after C.open；long；before D.closed；long；before
单项选择题 （）is the main reason that reduces the power advantage of a two-stroke engine over a same size four-stroke one to about（）
单项选择题 In a diesel engine, when the fuel is injected into the cylinder,（）
单项选择题 One of the differences between a two-stroke engine and a four-stroke engine is,（）
