单选题 (71) in the strength ofthe carrier signal is varied to represent binary 1 or 0.
(72) is a system that can map a name to all address and conversely an address to an name.
(73) is a three-way handshaking authentication protocol that it's packets are encapsulated in the point-to-point protocol
(74) is an approach that enables an ATM Switch to behave like a LAN switch.
(75) is an guided media which is made of glass or plastic and transmits signaIs in the form of light.

【正确答案】 A
【答案解析】[解析] 在幅频键控(ASK)调制中，载波的振幅随所表示的0、1变化；DNS是一种能够将名字映射为IP地址同时也可以将IP地址映射为名字的系统；CHAP是一种利用三次握手机制的认证协议，它的数据包被封装在点对点链路协议上；LANE是一种能够让ATM交换机象局域网交换机一样的方式：光纤是一种用玻璃纤维和塑料外套制成的传输介质，它上面以光的形式来传输信号。
【正确答案】 D
【答案解析】
【正确答案】 C
【答案解析】
【正确答案】 B
【答案解析】
【正确答案】 B
【答案解析】