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单选题
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
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