Which of the following statements is true of bulimia nervosa?

a. People with bulimia continue to want to lose weight even when they are underweight.

b. Bulimia is marked by weight fluctuations within or above normal ranges.

c. Those with bulimia are equally likely to be male or female.

d. If one twin is diagnosed with bulimia, the chances of the other twin sharing the disorder are greater if they are fraternal rather than identical twins.