一平面简谐机械波在媒质中传播时,若一媒质质元在t时刻的波的能量是10J,则在(t+T)(T为波的周期)时刻该媒质质元的振动动能是:()
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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