A. A CSU/DSU converts analog signals from a router to a leased line; a modem converts analog signals from a router to a leased line.
B. A CSU/DSU converts analog signals from a router to a phone line; a modem converts digital signals froma router to a leased line.
C. A CSU/DSU converts digital signals from a router to a phone line; a modem converts analog signals from a router to a phone line.
D. A CSU/DSU converts digital signals from a router to a leased line; a modem converts digital signals from a router to a phone line.
求解释 解释详细点 谢谢 本人英文不好
Modem把数字信号转换为相应的模拟信号，这个过程称为“调制”。经过调制的信肢核滑号通过电话载波传送到另一台计算机之前，也要经由接收方的Modem负责把模拟信号还原为计算机能识别的数字信号，这个过程我们称“解调”。
a modem converts digital signals from a router to a phone line. 调制解调器将转换从路由器到电话线的数字信氏正号。
CSU/DSU是连接终端和数字专线的设备，是数字信号到数字信号的转换。
A CSU/DSU converts digital signals from a router to a leased line CSU/DSU将转变从路由器到租用线路的数字信号。
其实，CSU/DSU是转变数字信号；而modem如果是从phone line到历腊router 则是将模拟信号转变成数字信号，从router到phone line则是将数字信号转变成模拟信号。
选：D
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