The correct option is A sweet
Adverbs modify verbs, adjectives or other adverbs. The underlined word is an adverb that modifies the noun 'chocolate'. Adverbs don't modify nouns, adjectives do, hence option D is incorrect. Option A is correct because the word is an adjective which describes the noun 'chocolate'. Option B is incorrect because it's a superlative and in order to use a superlative, the article 'the' should precede it. Option C is incorrect because the word 'sweets' itself is a noun which can't modify any other word.