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贵重物料应选择何种设备粉碎（ ）
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性生理发育是性心理和性行为的生理基础。
The voltage gain of the amplifier is the amplitude of the output voltage minus the amplitude of the input voltage.
Microphones are devices which detect sound signals and produce a voltage or a current which is proportional to the sound signal.
When you talk into a microphone, the micro without power will produce an electrical signal.
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