Which of the Following Best Explains the Lack of Well

Which of the following best explains the lack of well controlled studies on the effectiveness of treatment for anorexia nervosa?

A) Few people with anorexia are willing to seek treatment and there is a high drop-out rate when they do.
B) Few people with anorexia achieve full remission.
C) The high mortality rate with anorexia results in sample sizes too small to yield valid conclusions.
D) Few people with anorexia that are in treatment are willing to participate in studies.