Which statement is correct for muscle contraction?

Explanation

In contraction, the laterally projecting heads (cross-bridges) of the thick myosin myofilaments come in contact with the thin actin myofilaments and rotate on them. This pulls the thin myofilaments toward the middle of the sarcomere past the thick myofilaments. The Z-lines come closer together and the sarcomere becomes shorter. The length of the A-band remains constant. Myofilaments stay the same length. Free ends of actin myofilaments move closer to the centre of the sarcomere, bringing Z-lines closer together. I-bands shorten and the H-zone narrows to the level that it may disappear. A similar action in all the sarcomeres results in shortening of the entire myofibril, and thereby of the whole fibre and the whole muscle.