The correct answer is D. Fearful : Courageous.
In the original pair, “dunce” is the opposite of “clever”. In the other pairs, “flower” is not the opposite of “petals”, “worry” is not the opposite of “poor”, and “beautiful” is not the opposite of “attractive”.
A dunce is a stupid person, while a clever person is intelligent. A flower has petals, while a petal is a part of a flower. Worry is a feeling of anxiety or concern, while poor is having little or no money. Beautiful is having a pleasing appearance, while attractive is having the quality of attracting attention or interest.
In the pair “fearful : courageous”, “fearful” is the opposite of “courageous”. A fearful person is afraid, while a courageous person is brave.