Which of the following best completes the passage below?
A preliminary survey of online networking sites revealed that over 2,000 female users under age 18 are members of pro-anorexia discussion communities. This survey may overestimate the number of girls diagnosed with anorexia, however, since ________.
(C) 2008 GMAT Club - v01#22
1. many girls who are very thin could not be medically diagnosed as anorexic.
2. a large number of people with anorexia do not join online communities.
3. the survey was conducted according to a keyword search that included only the titles of registered communities, not their actual discussions.
4. doctors are unable to agree about the symptoms that constitute anorexia.
5. community members need not be diagnosed with anorexia in order to join.