When sweat evaporates from your skin the temperature of your skin decreases. this is because
a. energy is being applied to the skin.
b. the sweat is trapping molecules with a higher speed.
c. the water molecules with a higher speed are escaping .
d. the water molecules with a slower speed are escaping.

C - The water molecules with a higher speed are escaping

The temperature of a substance is a measure of the average kinetic energy of the molecules. Therefore as the higher speed molecules escape (by evaporation - that is the breaking of the bonds between the molecule and the rest of the liquid), the average KE of the skin decreases and hence the temperature decreases.

Well A is somewhat right, but energy is leaving the skin, and B is wrong because if the sweat was trapping the molecules with a higher speed your skin would not cool down, and C is wrong because the higher speed molecules is your water weight, but it is not on you to cool you down, so D is the right answer because the slower molecules are not leaving really, the molecules are on the skin too cool you down.