You are presented with the question "what gets contracted when fibers get shorter?" and the following answer choices: 
- nerves
 - h2o
 - veins
 - firm hugs
 - fur
 - biceps
 - the skin
 - density

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   