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（）.
- Aopen；short；after
- Bclosed；short；after
- Copen；long；before
- Dclosed；long；before