In (66) the strength of the carder signal is varied to represent binary 1 or 0. (67) is a system that can map a name to an address and conversely an address to an name. (68) is a three-way handshaking authentication protocol that it’s packets are encapsulated in the point-to-point protocol. (69) is an approach that enables an ATM Switch to behave like a LAN switch. (70) is an guided media which is made of glass or plastic and transmits signals in the form of light.

A．PPP

B．PAP

C．CHAP

D．LCP

备用液压系统低压指示灯在备用液压泵出口压力（）

A.减小到1000PSI时亮，增大到1200PSI时灭

B.减小到1300PSI时亮，增大到1600PSI时灭

C.减小到1600PSI时亮，增大到2000PSI时灭

D.减小到2000PSI时亮，增大到3000PSI时灭