You are presented with the quiz "Most canyons are formed by rivers flowing and what type of erosion?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "most canyons are formed by flowing rivers through erosion over long periods of time" and "geological erosion is natural occurring erosion over long periods of time". 

So, what's the best answer to the question?


 

    geological       