Fact 1: Tectonic plates being pushed together causes earthquakes.

Fact 2: Earthquakes are long preceded by tectonic shifts.

Given the two facts above, answer the question "earthquakes are caused by shifts in what?" with the following options: 
- earth
 - volcanoes
 - rocks
 - plates
 - Movement
 - ground
 - rain
 - lightning


 

    plates     