Hey there Jacob!
Well, one reason why matter would actually be moving within the earth would actually be basically because of (energy) and matter put together. Because of energy, this would be why matter would move.
But, from your option's listed above, your answer would be stated differently.
The other reason why matter would move would be because (The Earth's interior is hot..) Because it is more denser, this allow's for the energy to flow right through and so that matter would be able to move.
Your correct answer would be . . . .
[tex]\boxed{\boxed{The \ Earth's \ interior \ is \ hot.}}[/tex]
Hope this helps.
~Jurgen
