The correct answer is A. Antisocial.
Gregarious means sociable and outgoing. Antisocial means not sociable or outgoing; not wanting to be with other people. Glorious means very impressive or splendid. Horrendous means extremely bad or unpleasant. Similar means alike or identical.
Gregarious people enjoy being around others and are often the life of the party. They are usually good at making friends and keeping them. Antisocial people, on the other hand, prefer to be alone and avoid social interaction. They may be shy, introverted, or have social anxiety. Glorious things are impressive and cause admiration. Horrendous things are extremely bad or unpleasant. Similar things are alike or identical.