Margaret's Appetite Has Decreased Markedly Over the Course of the Semester

Margaret's appetite has decreased markedly over the course of the semester, resulting in a weight of 100 lbs. on her 5'9" frame. Her roommate has noticed that she tends to wear layers of clothing even in warm weather and frequently complains about her weight. If Margaret were referred for evaluation for an eating disorder, what percent of ideal body weight would be used as a criterion for excessive weight loss?

A) 35%
B) 50%
C) 65%
D) 85%