ANS:D - air is fully saturated.

When the dry bulb temperature and wet bulb temperature of moist air are the same, it means that the air is fully saturated. This is because the wet bulb temperature represents the temperature to which the air can be cooled by the evaporation of water until it reaches saturation. Therefore, if the dry bulb temperature (the actual air temperature) matches the wet bulb temperature (the temperature achieved through evaporative cooling), it indicates that the air is already at its saturation point, and further cooling would cause water vapor to condense out of the air. So, the correct statement is: "Air is fully saturated."