Correct option is D
On a psychrometric chart, the vertical and uniformly spaced lines represent the dry bulb temperature. The dry bulb temperature is the temperature of the air measured by a regular thermometer exposed to the air but shielded from radiation and moisture. It is called "dry bulb" because the thermometer is dry and does not account for the moisture content in the air. This temperature is a key parameter in air-conditioning and heating calculations, as it directly influences comfort levels in indoor environments.
