质量为4.0 ×10³Kg汽车，发动机的额定功率P=40Kw，行驶过程中所受阻力为2.0×10³N，则汽车能达到的最大速度为         m/s。

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 （1）. This, in turn, limits the data rate that can be carried on the transmission （2）. A square wave has an infinite number of frequency components and hence an infinite （3）. However, the peak amplitude of the kth frequency component, kf, is only l/k, so most of the （4） in this waveform is in the first few frequency components. In general, any digital waveform will have（5） 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.

（4）是（）

A.frequency

B.energy

C.amplitude

D.phase