Chiara, a 14-year-old, is of average height but weighs only 80 pounds. She has lost 30 pound over the last six months by eating very little and running five miles a day. She is determined not to become overweight and ignores her parents' suggestion that she should eat well-balanced meals. Chiara suffers from .a. bulimia nervosa. b. obesity. c. an abnormally low set point. d. anorexia nervosa.