What is the difference between a CSU/DSU and a modem?

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 from a 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．

【正确答案】 D

【答案解析】csu/dsu和modem的不同点是什么？
考点分析：这道题考的是CSU/DSU和modem的基本作用。CSU/DSU是把数字信号从路由转换到租用线路上，modem是进行数模转换的设备。CSU/DSU一般是专线，MODEN是将模拟信号与数字信号转换。