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问题 单项选择题

在简谐波传播过程中，沿传播方向相距为1/2λ（λ为波长）的两点的振动速度必定有下列中哪种关系？（）

A.大小相同，而方向相反

B.大小和方向均相同

C.大小不同，方向相同

D.大小不同，而方向相反

答案

参考答案：A

单项选择题

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.

A square wave has an infinite number of frequency components and hence an infinite（）

A．source

B．bandwidth

C．energy

D．cost
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单项选择题

把需要详细表达的建筑局部用较大比例画出，称为建筑（）。

A、剖面图

B、平面图

C、详图

D、立面图
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