Why is humidity generally low in desert regions?

Correct answer: Water sources for evaporation are very limited

Correct answer: A. Humidity is the amount of water vapour in the air. Most desert regions have very limited rivers, lakes, or other exposed water surfaces. Because the supply of liquid water is small, evaporation usually adds less vapour to the atmosphere. Hot desert air may have a high capacity to hold vapour, but that does not mean it actually contains much vapour; this is an important distinction. Option A correctly identifies the limited moisture supply. Option B is wrong because persistent dense clouds would generally indicate more atmospheric moisture, not the usual desert condition. Option C is wrong because daily heavy rainfall would add water and raise humidity. Option D is wrong because regular moist sea winds would also increase moisture. Memory cue: low humidity is linked to little water vapour, not simply to high temperature.