单选题 Although a given waveform may contain frequencies over a very broad range, as a practical matter any transmission system will be able to accommodate only a limited band of ______. This, in turn, limits the data rate that can be carried on the transmission ______. A square wave has an infinite number of frequency components and hence an infinite ______. However, the peak amplitude of the kth frequency component, kf, is only 1/k, so most of the ______ in this waveform is in the first few frequency components. In general, any digital waveform will have ______ bandwidth. If we attempt to transmit this waveform as a signal over any medium, the transmission system will limit the bandwidth that can be transmitted.

【正确答案】 C

【答案解析】[解析] 虽然一个给定的波形包含了很宽的频率范围，但是任何实际的传输系统只能够通过有限的频带(frequencies)。这样，就限制了传输介质(medium)可以承载的数据速率。一个方波包含了无限多的频率成分，因而也具有无限的带宽(bandwidth)。然而，第庀个频率成分的峰值幅度k _f 只是1/k，所以波形的大部分能量(energy)只包含在前面的少数频率成分中。一般来说，任何数字波形都有无限(infinite)带宽。如果我们试图在某种介质上传输这种波形信号，则传输系统实际上会限制可以发送的带宽。