The relaxation of skeletal muscle fibers and the skeletal muscle, itself, begins with the motor neuron, which stops releasing its chemical signal, ACh, into the synapse at the neuromuscular junction. The muscle fiber will repolarize. What is the next step in relaxation? A) The actin-binding sites on the thin filaments are reshielded. B) ATP-driven pumps move Ca++ out of the sarcoplasmic reticulum. C) Troponin and tropomyosin revert back to their original positions on the actin fibers. D) The gates in the sarcoplasmic reticulum where Ca++ was being released are closed.