Digital data can also be represented by (71)signals by use ofa modem. The modem converts a series of binary voltage (72) into an analog signal by encoding the digital data ontoa carrier frequency. The resulting signal occupies a certam spectrum of (73) centered about the carTier and may be propagated acrossa medium suitable for that carrier. The most common modems represent digital data in the voice(74)and hence allow those datato be propagated over ordinary voice-grade (75 )lines At the other end of the line, another modem demodulates the signal to recover the original data (71)
A.analog B.digital B.Modem D.electric
【参考答案】
A 数字数据也可以通过调制解调器用模拟信号来表示。调制解调器把数字数据编码为一种载波频率，从而可以把二进制电压序......