You are presented with the question "What makes the pupil change sizes?" and the following answer choices: 
- electrically
 - sun's heat
 - sweating
 - It expands
 - The iris
 - nerves
 - environment
 - heat

Now knowing that light enters the eye through an opening called the pupil and light enters the eye through the pupil, and the pupil is made larger or smaller by the iris, choose the best answer.


 

     The iris    