在握手时应注意：要专心、面带微笑，要稍稍用力，停留（）秒。
A、3
B、9
C、3-5
D、3-9
参考答案：C
30/32路PCM每一路的码率是多少？总码率又是多少？
An engineer designed a ball so that when it was dropped, it rose with each bounce exactly one-half as high as it had fallen. The engineer dropped the ball from a 16-meter platform and caught it after it had traveled 46.5 meters. How many times did the ball bounce ？（）
A. 5
B. 6
C. 7
D. 8
E. 9
