If dry and wet bulbs show almost the same temperature, what does it mean?

Correct answer: Air is nearly saturated

Correct answer: A, the air is nearly saturated. The wet bulb becomes cooler only when water evaporates from its moist covering. If the surrounding air already contains nearly as much water vapour as it can hold at that temperature, very little additional evaporation takes place. Consequently, the wet bulb is hardly cooled and its temperature is almost the same as the dry-bulb temperature. This small wet-bulb depression indicates high relative humidity and air close to saturation. Option B is wrong because completely moisture-free air would cause strong evaporation and a large temperature difference. Option C is wrong because high temperature alone does not prove that the air is dry; the readings must be interpreted together. Option D is wrong because extremely rapid evaporation would cool the wet bulb strongly and create a large difference. Memory cue: equal readings mean little evaporation, therefore moist air.