Option 1: eager -> This is a synonym of "avid," meaning enthusiastic or keen, not an antonym.
Option 2: assertive -> This means confident and forceful, which is unrelated to the meaning of "avid."
Option 3: aural -> This relates to hearing or the ear, completely unrelated to "avid."
Option 4: averse -> This means having a strong dislike or opposition to something, the direct opposite of "avid" (keen interest).
Hence, Option 4: averse -> "Avid" means having keen interest or enthusiasm, while "averse" means having a strong dislike or opposition to something, making them perfect antonyms. -> correct