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

Fact 2: Fronts define the boundaries between air masses.

Given the two facts above, answer the question "Movement of what causes local weather changes?" with the following options: 
- wind
 - energy
 - influenza
 - Pacific
 - an object
 - fronts
 - rivers
 - heat


 

      fronts   