Answer the following question given this paragraph: 

Each muscle fiber contains hundreds of organelles called myofibrils . Each myofibril is made up of two types of protein filaments: actin filaments, which are thinner, and myosin filaments, which are thicker. Actin filaments are anchored to structures called Z lines (see Figure below ). The region between two Z lines is called a sarcomere . Within a sarcomere, myosin filaments overlap the actin filaments. The myosin filaments have tiny structures called cross bridges that can attach to actin filaments.


Q: Hundreds of organelles called myofibrils, made up of two types of protein filaments, are contained in each fiber of what?

 Choices:

- bone

- hair

- cartilage

- muscle

A:
muscle
