The correct option is C inversely proportional
Clothes dry when water evaporates from them.
On a rainy day, there is a lot of water content (humidity) in air.
With more humidity, the water intake capacity of air decreases.
Thus, the rate of evaporation decreases and it takes longer for the clothes to dry out on a rainy day.
Hence, the rate of evaporation is inversely proportional to the humidity in the air.