● 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__(71)__.This， in turn，limits the data rate that can be carried on the transmission__(72)__. A square wave has an infinite number of frequency components and hence an infinite __(73)__.However， the peak amplitude of the kth frequency component， kf， is only 1/k， so most of the__(74)__in this waveform is in the first few frequency components. In general， any digital waveform will have__(75)__bandwidth. If we attempt to transmit this waveform as a signalover any medium， the transmission system will limit the bandwidth that can be transmitted.

（71）A．frequencies 

B．connections

C．diagrams  

D．resources

（72）A．procedure 

B．function 

C．route

D．medium

（73）A．source  

B．bandwidth  

C．energy

D．cost

（74）A．frequency

B．energy   

C．amplitude

D．phase

（75）A．small  

B．limited

C．infinite 

D．finite