Synonyms are words which have the same or nearly the same meaning in the same language.
Antonyms are words which have opposite meaning in comparison to the other.
Option D)sweet is correct as the word sweet means pleasing in general; delightfuland the word sarcastic means marked by or given to using irony in order to mock or convey contempt.
Both the words are opposite of each other.
The other options are not correct as they do not have the opposite meaning to the given word.