Millions of people in the United States are affected by
eating disorders, more than 90% of those afflicted are adolescents or young women.
Let us not mistake that the people are affected by eating a food dish known as 'disorders'. Actually eating is an adjective modifying the noun 'disorders' such as indigestion, excess acidity or some such thing.
A. eating disorders, more than 90%--- this is a comma splice
B. eating disorders; more than 90% -- This is the correct answer
C. eating disorders, of which more than 90%--- this means 90% of the disorders are people
D. Eating disorders. Ninety percent more ---. The second clause misses the relatedness with the first clause because of the period. It is also not clear what the choice means to convey by saying 'ninety percent more" are those afflicted are young people. A minor point is also that whenever the number exceeds ten, it is normally written with numbers rather than with words.
E. Eating disorders, over 90% ---- This is also a comma splice