Great response.
I'll just add that this is essentially an Argument by Analogy. In this case, the analogy is "it's fair to compare what happened in the past to what will happen in the future".
To strengthen an analogy, we want to hear ideas of "sameness". To weaken one, we want to hear ideas of "difference/distinction".
(E) is "sameness" ... a 'continuation of one of the past courses'
(C) is "sameness" ... the student's study setting has not changed
(A), the correct answer, WEAKENS because it presents "difference/distinction". She previously studied alone. She now will be studying with others. It actually makes it seem like the student might be more likely to get an A this time around (given her stellar study buddies).
(D) emphasizes the "sameness" of her previous track record. It wasn't 7 B's and 5 other grades. It was 11 B's and only 1 other grade (more "sameness").
(B), in a weird way, protects against "difference/distinction". If the 12 previous classes had been within a narrow range of subject matter, it would be more likely that her new course could be DIFFERENT. Since (B) tells us the 12 previous classes covered a broad range, there's less of a way for the new class to be DIFFERENT. After all, her 12 previous classes were all different. So a new, different class is really just the same.
Sorry, I know that last line sounded either zen, contradictory, or just confusing but I couldn't resist.