主动齿轮轮齿数为17,从动齿轮轮齿数为34,则两轮传动比为　( A.
1/2 B.
1/3 C.
2 D.
3

A．shout out with the largest volume
B．put the microphone near to your mouth as close as possible
C．murmur to yourself
D．put the microphone near to your mouth but with a distance of about 3-5cm