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 A)facilitate is correct as the word hinder means make it difficult for (someone) to do something or for (something) to happen and the word facilitate means make (an action or process) easy or easier. Both the words are opposite of each other.
The other options are not correct as stimulate, consistent and eradicate are not the opposites of the word hinder.