The word “although” means that two

The word “although” means that two things are related in a negative or opposite
way. The correct answer choice will set up an opposite relationship between
Kate’s lengthy report and her presentation. If her presentation was not lengthy, it
must have been (A) brief. “Brief” is the opposite of “lengthy.” The correct answer
is (A).
The other answer choices do not set up opposite relationships. It is possible that
both the report and the presentation were (B) neutral, (C) mundane, (D) straightforward, or (E) elaborate. None of these words deal with length, so there
is no contradiction between being lengthy and having any of these other
characteristics. Therefore, these answer choices are incorrect