You are presented with the question "What is a common cause for the development of a lake bed?" and the following answer choices: 
- paralysis
 - thunder and lightning
 - flowing river
 - erosion
 - rainfall
 - flooding
 - Sediment
 - fulmination

Now knowing that avalley is formed by a river flowing and most of the valley floors are old lake beds, choose the best answer.


 

   flowing river      