複選題44. Which statement best describes the power stroke of muscle contraction? (A) The myosin head bends, pulling the thick filament toward the center of the sarcomere. (B) The myosin head bends, pushing the thin filament toward the center of the sarcomere. (C) The actin head bends, pulling the thin filament toward the center of the sarcomere. (D) The actin head bends, pulling the thick filament toward the center of the sarcomere. (E) The myosin head bends, pulling the thin filament toward the center of the sarcomere.