单选题Relative humidity is the percentage of water vapor that is in the air as compared to the maximum amount it can hold at（）.Aa specific barometric pressureBa specific temperatureCa specific wind speedDany time
单选题
Relative humidity is the percentage of water vapor that is in the air as compared to the maximum amount it can hold at（）.
A
a specific barometric pressure
B
a specific temperature
C
a specific wind speed
D
any time
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