Fact 1: The movement of an air mass over Earth 's surface causes local weather changes.

Fact 2: When air masses meet, fronts are formed.

Given the two facts above, answer the question "What cause local weather changes?" with the following options: 
- Movement
 - earthquakes
 - fronts
 - wind
 - chemicals
 - flooding
 - trees
 - thunder


 

   fronts      