Answer: Option B
Explanation:
Myofibrils are very fine contractile fibers which extends in parallel to the columns along the length of the striated muscles fibres.
They are made of thick and thin myofilaments because of which the muscles appear striped.
The thick filaments in the muscles are composed of actin along with two other muscle protein known as tropomyosin and troponin. They help in contraction of muscles.