Final answer:
Folk songs, folk dances, and folk musical instruments are supplementary to each other as they form an integral part of folk culture.
Step-by-step explanation:
Folk songs, folk dances, and folk musical instruments are all supplementary to each other because they are interconnected and form an integral part of folk culture. Let's consider an example of a traditional folk dance, like the Irish jig. The music played during the jig is typically a folk song, and the instruments used, such as the fiddle or tin whistle, are folk musical instruments. The dance is influenced by the rhythm and melody of the music, creating a harmonious relationship between the three elements.