What is involved in a musclecontraction?A. Myofibrils in the muscle shorten and lengthen to makethe muscle contract and extend.B. Actin and myosin come in and out of the cell to make itthicker or thinner which changes its length.C. The gap junctions between the cells pull them closertogether which shortens the muscle.D. The extra nuclei trigger nerves to stiffen the musclesand make them shorter.