当选择拾振器做测位移使用时,要使拾振器的相对位移振幅Y0与被测振动体的振幅X0之比趋近于1,则要求频率比u和阻尼比D满足:( )
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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