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 B)keep is correct as the word keep means have or retain possession ofand the word abandon means cease to support or look after (someone); desert.
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.