Fact 1: Muscle contraction occurs when muscle fibers get shorter.

Fact 2: Muscles are bundles of fibers that can contract.

Given the two facts above, answer the question "What contracts as it gets shorter?" with the following options: 
- layers of fat
 - Epidermis
 - Veins and arteries.
 - Shortstop
 - Labor
 - Contracts
 - the body's largest organ
 - Bundles of fibers


 

        Bundles of fibers 