You are presented with the question "Fog is formed when" and the following answer choices: 
- summer end
 - evaporation
 - Winter
 - movement
 - air cools
 - Wet weather
 - rainy
 - dry and hot

Now knowing that fog is formed by water vapor condensing in the air and when air cools, the water vapor in the air condenses.", choose the best answer.


 

     air cools    