If relative humidity is very high at a place, why will sweat dry slowly?

Correct answer: The air is already nearly saturated with water vapour

Direct answer: A, the air is already nearly saturated with water vapour. Sweat cools the body mainly when liquid sweat evaporates from the skin and takes heat away. For evaporation to continue rapidly, the surrounding air must be able to accept more water vapour. At very high relative humidity, the air is already close to its maximum capacity at that temperature. The difference between the vapour at the skin and in the surrounding air is therefore small, so evaporation slows and sweat remains on the skin longer. B is wrong because high humidity does not automatically lower sweat below freezing. C is wrong because ordinary high humidity does not turn sweat into ice. D is wrong because humidity does not completely block sunlight; even if sunlight is reduced by clouds, that is a separate issue. Memory cue: humid air accepts less sweat vapour, so cooling by evaporation becomes less effective.