The correct answer is: D. Both (b) and (c).
At night, the sun is not shining, so there is no heat being added to the air. This causes the air temperature to drop. However, the water vapor in the air does not cool as quickly as the air. This is because water vapor has a high heat capacity, which means it can hold a lot of heat. As the air cools, the water vapor starts to condense into liquid water. This process releases latent heat, which warms the air. This warming effect of condensation prevents the air temperature from dropping below the dew point temperature.
Option A is incorrect because dew does not absorb heat. Dew is simply water vapor that has condensed into liquid water. It does not have any special properties that allow it to absorb heat.
Option B is incorrect because saturation vapor pressure does not always increase at night. Saturation vapor pressure is the maximum amount of water vapor that can be in the air at a given temperature. It is affected by temperature, but it is not affected by time of day.
Option C is correct because at saturation, latent heat of condensation is released into the air. This latent heat warms the air and prevents the temperature from dropping below the dew point temperature.