Antonyms are words that have contrasting, or opposite, meanings.
Choice A is correct. Garrulous means 'extremely talkative on trivial matters' the opposite being reticent meaning 'not ready to reveal one's thoughts or feelings readily'. For example: She was extremely reticent about her personal affairs. Choice B means 'someone who speaks very softly. Choice C means 'not fighting'. choice D means 'someone who is gives readily'. Choice B, C and D are wrong.