Fact 1: Faulting of rock in Earth 's crust causes earthquakes.

Fact 2: Earthquakes and volcanoes are violent proof of Earth's shifting crust.

Given the two facts above, answer the question "Shifting in the Earth's crust are caused by what?" with the following options: 
- Greenhouse gases
 - rock beds
 - friction
 - avalanches
 - fault in rocks
 - no movement in the crust
 - Movement
 - Time and energy


 

     fault in rocks    