Concept:The word "Juvenile" means relating to young people or showing immature, childlike behavior. Its synonym is a word with a similar meaning.Explanation:"Juvenile" describes something connected to youth or childishness. For example, a juvenile book is for young readers. Among the options, "Childish" directly refers to behavior like that of a child, often implying immaturity. This matches the sense of "Juvenile". The other options are opposites: "Ancient" means very old, "Grown-up" means adult, and "Elder" means older person. Therefore, "Childish" is the correct synonym.Answer:A. Childish