The word 'joyful' is a synonym for 'happy'. Both words describe a state of being pleased and content. Synonyms are words that have the same or similar meanings. In contrast, 'angry', 'tired', and 'sad' have meanings that do not align with 'happy'. These words describe emotions or states that are quite different from happiness. For example, 'angry' implies being upset, 'tired' refers to a state of fatigue, and 'sad' indicates unhappiness. Therefore, 'joyful' is the correct synonym.
