题目：
A typical application of this (71) is ADSL. It is emerging as the technology for home-and small-office Internet connectivity. It provides either 1.5 Mb/s～8 Mb/s from the network to the user and 64 kb/s～512 kb/s in the reverse direction depending on the distance, 12000 or 18000 feet. The different speed for each direction gives it the (72) label. ADSL is designed to take advantage of the fact that video-on demand, telecommuting, and Internet access traffic are inherently asymmetrical. The user (73) a brief message up to the network and receives a ton of data coming back, either a movie or a piece of data download. Under such a scenario, low-speed traffic to the network is just fine. ADSL .delivers high (74) where you need it and only uses a single copper pair. Through multiplexing, it also reserves (75) of the bandwidth for POTS.
A．2 kHz
B．4 kHz
C．16 kHz
D．64kHz
答案：
参考答案：B
解析：[参考译文] FTTC的一种典型应用是ADSL(非对称数字用户线路)。ADSL正在作为家庭和小型办公室的Internet连接技术出现。依据距离的不同，对于12000英尺或18000英尺，它提供了从网络到用户的1.5Mb/s或8Mb/s和从用户到网络的64kb/s或512kb/s的高速连接。在两个方向有不同速度使它得到了不对称的称号。ADSL的设计利用了这样一个事实：视频点播、在家工作和Internet信息访问等应用本来就是不对称的。用户向网络发送一个简短的报文，而收到大量的数据，或是一部电影或是数据下载。在这样的情况下，向网络发低速信息流是没问题的。ADSL在用户需要之处给出了大带宽，并且只用一对铜线。通过多路复用，它还能为打普通电话保留4kHz的带宽。
