Which statements are true regarding ISDN channels?()
A. Each B channel can transmit up to 64 kbps
B. The ISDN B channel carries voice or data
C. The ISDN D channel transmits control information.
D. The D channel transmission rate varies depending on the service used.
E. HDLC or PPP can be used to encapsulate D channel information.
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背向式跳高助跑是采用()
A. 直线式
B. 弧形
C. 斜线
D. S型
曲柄摇杆机构中构件间的接触形式是()
A. 移动副
B. 转动副
C. 螺旋副
D. 凸轮副