You are presented with the question "what contracts when fibers get shorter?" and the following answer choices: 
- strength
 - strong
 - h2o
 - bushes
 - density
 - wheat
 - firm hugs
 - biceps

Now knowing that muscle contraction occurs when muscle fibers get shorter and muscles in the upper arm called biceps are used to flex the arm, choose the best answer.


 

        biceps 