You are presented with the question "What condenses in clouds to cause rain?" and the following answer choices: 
- evaporation
 - chlorofluorocarbons
 - Organic compounds
 - carbon dioxide
 - a gas in the air
 - Chemical energy
 - peachleaf willow
 - flooding

Now knowing that water vapor condensing in clouds causes rain and water vapor is a gas in the air, choose the best answer.


 

     a gas in the air    