Hi imskpwr,
While this example question is a bit wordy and uses some odd wording ("to suspect"), you can remove most of the words and still have the true meaning of the question:
"Which....if true....supplies the best reason.....that the....new courses will increase interest in the...Academy?"
This is, in all likelihood, a STRENGTHENER.
CONTEXT is important though. Since the question uses the phrase "to suspect" (which has some negative connotations), it's possible that the prompt that precedes this question describes a situation in which the new courses DECREASE interest in the Academy. If that is the case here, then you'd be looking for an answer that weakens the logic presented in the prompt.
Can you submit the entire question?
GMAT assassins aren't born, they're made,
Rich