A 21-year-old primigravida has an emergency cesarean delivery under general anesthesia because of unanticipated fetal distress. One postoperative intervention is to assist her to turn every 2 hours. Which of the following conditions is this intervention intended to prevent ？（）
A．Pressure ulcers.
B．Muscular stiffness.
C．Respiratory complications.
D．Venous stasis.