Fact 1: Uneven heating of the Earth 's surface cause wind.

Fact 2: Wind is a movement of air, and air is invisible.

Given the two facts above, answer the question "Uneven heating of the Earth 's surface causes a movement of what?" with the following options: 
- wind
 - light
 - air
 - soil
 - sand
 - asteroids
 - cookies
 - Aves


 

   air      