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问题 单项选择题

热爱家乡，热爱祖国，树立为中 * * 复兴、为人类文明和社会进步而努力学习化学的责任感和使命感属于高中化学课程的（）目标。

A.知识与技能

B.过程与方法

C.知识与能力

D.情感·态度·价值观

答案

参考答案：D

单项选择题 A1/A2型题

以下哪种物质为骨吸收促进因子，抑制骨胶原合成（）

A.前列腺素

B.白细胞介素

C.肿瘤坏死因子

D.成纤维细胞生长因子

E.以上都不是
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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 （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
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