Correct Answer: C
Explanation:
III only. They first sentence makes it clear that neither Mr. Tibbitts nor Ms. Mondragon will teach classes during the summer. However, nothing in the passage assures that Mr. Parnelli will also decide not to teach classes during the summer (…. If both Ms. Mondragon and Mr. Parnelli….), and therefore we cannot conclusively deduce that Professor Revlon will teach classes during the summer. Only by knowing that Mr. Parnelli will not teach summer classes (III) do we then have all the pieces in place to conclude that Professor Revlon will teach summer classes and therefore cause confusion in the administrative office.