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 C)strangers is correct as the word strangers means a person whom one does not know or with whom one is not familiarand the word kith means one's relations.
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.