单选题In a four-stroke engines the camshaft rotates at （）.Ahalf the engine rotational speedBtwice the engine rotational speedCthe engine rotational speedDfour times the engine rotational speed
单选题
In a four-stroke engines the camshaft rotates at （）.
A
half the engine rotational speed
B
twice the engine rotational speed
C
the engine rotational speed
D
four times the engine rotational speed
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