You are presented with the question "How do we track canyon changes?" and the following answer choices: 
- LEDs
 - wind
 - forces
 - river
 - slow
 - Pins
 - Raft
 - three

Now knowing that most canyons are formed by flowing rivers through erosion over long periods of time and erosion was monitored by means of erosion pins, choose the best answer.


 

      Pins   