The correct answer is A. Hostile.
Antonyms are words with exactly the opposite meaning. Friendly means well-disposed, behaving or acting as a friend, amicably. On the other hand, hostile means acting as an enemy, in an unpleasant and non-friendly way.
Pleasant and welcoming would be, in a way, synonyms for friendly - that is, words with the same or similar meaning. Timid means shy or fearful, so it has nothing to do with friendly.
