Fact 1: Water vapor cooling causes that water vapor to condense.

Fact 2: All lenses are anti-fog coated to eliminate condensation.

Given the two facts above, answer the question "What could cause lenses to fog?" with the following options: 
- energy of moving objects
 - Transpiration from plants
 - Water evaporating
 - heating liquids
 - Water vapor cooling
 - Ice sublimating
 - scattered light
 - The atmosphere


 

     Water vapor cooling    