You are presented with the question "What grinds rocks over time?" and the following answer choices: 
- deltas
 - erosion
 - Time and energy
 - weathering
 - Echinoderm.
 - deuterostomes
 - amoebae
 - bullfrogs

Now knowing that rocks interacting with wind over long periods of time causes weathering and winds grind down rocks, choose the best answer.


 

    weathering     