Answer: C - Full Saturated
Zero wet-bulb depression signifies the air is fully saturated.
The wet-bulb depression (WBD) is the numerical difference between the dry-bulb temperature and the wet-bulb temperature.
WBD = DBT -WBT
When the air is completely saturated, it reaches the saturation line, where the relative humidity is 100% and the dry bulb, wet bulb, and dew point temperatures are all the same. At this instant, wet-bulb depression is zero. It means that the zero wet-bulb depression signifies the air is fully saturated.