Thanks for the question! So let’s take a look at this stimulus. We’re told that it’s not good for a university to have very big or very small classes, or professors with very light or very heavy teaching loads. And then we’re told that crowded classes and overworked faculty are bad because it hurts the university’s ability to recruit and retain students and faculty.
OK, well, now the question is asking us to add a premise to the argument to help justify the conclusion. And the conclusion here is going to be the first sentence. But notice that the premise we’re given just tells us why it’s bad to have very large classes and professors with very heavy teaching loads. But the conclusion isn’t just about those; it’s also about classes are very small and professors with very light teaching loads. So the premise we add has to explain why those are bad in order to complete the stimulus.
Now take a look at (C), which does exactly this. It tells us that very small class sizes or very light teaching loads are bad because they indicate incompetence in classroom instruction. This helps us complete the other half of the conclusion that was previously unaddressed, and so helps justify the conclusion.
Hope this helps! Feel free to ask any other questions that you might have.
