Answer:
The answer is A.
Step-by-step explanation:
First, let`s define antonyms - they are words of the opposite meaning (small-large)
Prodigious means being immense, great, stunning, amazing and etc. So other answers: exceptional, stupendous and superior can relate in some way with prodigious, so we can say they are synonyms ( words of the same or similar meaning).
The only word that means the opposite is ordinary, so this is the antonym we are looking for.