You are presented with the question "What creates metamorphic rock?" and the following answer choices: 
- gravity
 - calcite
 - Earth's core
 - engine
 - desire
 - a hydraulic system
 - forces
 - flow of electrons

Now knowing that extreme heat and pressure change rock into metamorphic rock and most of the heat for the Earth comes from the core, choose the best answer.


 

   Earth's core      