In the second sentence, the adjective is delighted. In the third sentence, the adjective is large. The first sentence doesn't contain an adjective.
Whale sharks are one of the biggest fish reaching lengths of about 40 feet
I have just taken the quiz. B was incorrect.
For future students the answer is
A. Motif
(K12 studentsssss)
The resolution/conclusion is what you're looking for
Hope I helped :)