Fact 1: Fog is formed by water vapor condensing in the air.

Fact 2: Fog is essentially very low clouds, consisting of water vapor cooling and beginning to condense.

Given the two facts above, answer the question "What happens when water vapors cool down?" with the following options: 
- colder weather
 - Fog is formed
 - Heat energy
 - evaporation
 - chemical changes
 - Something to move
 - prolactin release
 - Energy.


 

  Fog is formed       