Option 1: Nervous -> Refers to anxiety or unease, not the direct opposite of brave/valiant.
Option 2: Kind -> Relates to compassion and gentleness, unrelated to courage or bravery.
Option 3: Coward -> Describes someone who lacks courage, the direct opposite of valiant.
Option 4: Brave -> This is a synonym of valiant, not an antonym.
Hence, Option 3: Coward -> Valiant means showing courage and bravery, so its antonym would be someone who lacks these qualities, which is a coward -> correct