The Hubble Flow, Demonstrating the Expansion of the Universe, Occurs

The Hubble flow, demonstrating the expansion of the universe, occurs

A) between galaxies in clusters, clusters in superclusters, and superclusters in wider regions of space.
B) only between superclusters of galaxies.
C) between stars in galaxies, galaxies in clusters, clusters in superclusters, and superclusters over wider regions of space.
D) between clusters of galaxies in superclusters and between superclusters over wider ranges of space.