The correct answer is: C. Decrease.
Relative humidity is the ratio of the amount of water vapor in the air to the amount of water vapor that the air could hold at that temperature. As the air temperature increases, the air can hold more water vapor. This means that the relative humidity will decrease.
For example, if the air temperature is 20 degrees Celsius and the relative humidity is 60%, this means that the air contains 60% of the water vapor that it could hold at that temperature. If the air temperature increases to 25 degrees Celsius, the air can now hold 75% of the water vapor that it could hold at 20 degrees Celsius. This means that the relative humidity will decrease to 40%.
The dew point temperature is the temperature at which the air is saturated, or at 100% relative humidity. If the air temperature is below the dew point temperature, the air will be able to hold more water vapor. If the air temperature is above the dew point temperature, the air will release water vapor.
I hope this helps! Let me know if you have any other questions.