What is OA and OE?

Also, please mention the source.

IMO:

Honor students are those who have high grades/achievement in the class.

What I Understand from B :

Honor students, who have altered their diets => (It means that they are among the college students on which the research has been done)

These Honor Students, who have altered their diets, didn't change their study habits and haven't scored better on average than other students, especially other honor students

The higher score of Honors students would had been the case if the research had been correct to say that the students who have altered their diet outperform others)

==> IMO it implies that study habits is important in improving the grade/performance as shown in the study of honor students and supports the research conclusion that nutritional diet doesn't affect the grades.

As said above, Comparison of two honor students is important here, for it implies that the nutritional effect doesn't work on honor students as they do not change their study habits.

This could be the reason for the other students too.

So, IMO, B is considering subset of students to prove that study is in fact accurate.

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Consider kudos for the good post ...

My debrief : http://gmatclub.com/forum/journey-670-to-720-q50-v36-long-85083.html