A.the mass of water vapour present in 1 m³ of dry air
B.the mass of water vapour present in 1 kg of dry air
C.the ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure.
D.the ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure
Answer: D
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