A) it changes conformation,twisting tropomyosin and exposing the actin-myosin binding site. B) ion channels open and sodium rushes into the muscle cells. C) it allows tropomyosin to bind actin. D) it changes conformation,exposing the ATP binding site and allowing the actin-myosin bond to break. E) ATP binds to the myosin head,allowing myosin to attach to actin.