You are presented with the question "What is not caused by riding a bike?" and the following answer choices: 
- momentum
 - flooding
 - coal
 - disease
 - speed
 - Allergies
 - litter
 - exercise

Now knowing that riding a bike does not cause pollution and visual pollution caused by littering is pollution, just as is water pollution and air pollution, choose the best answer.


 

       litter  