Concept:Ife art is best known for its naturalistic sculptures made from fired clay and metal.Explanation:The Ife civilization produced highly refined terra cotta heads and bronze heads.These works are famous for their realistic human features and artistic skill.Items like quartz stools and carved granite figures also existed, but the heads are the most celebrated achievement.This makes terra cotta and bronze heads the defining feature of Ife art.Answer:A. use of terra cotta and bronze heads.