The correct answer is D) relative humidity and dew point. By using the dry bulb and wet bulb temperatures from a psychrometer, you can determine the relative humidity and dew point of the air. The dry bulb temperature is the actual air temperature, while the wet bulb temperature is lowered by the evaporative cooling effect. Comparing these two values on a psychrometric chart allows you to determine the relative humidity and dew point, which are important meteorological parameters. The other options are incorrect because they do not directly relate to the function of a psychrometer. Wind chill and wind speed are not determined from dry and wet bulb temperatures, and atmospheric pressure is measured by a barometer, not a psychrometer.