What specific piece(s) of evidence for dark matter do astronomers find? Choose all that apply.
a. They calculate more mass in various large-scale structures than is visible as luminous matter.
b. They observe large dark regions between galaxies.
c. Galactic rotation curves do not match expectations based on mass and radius.
d. X-ray halos in galaxy clusters have too much pressure to be gravitationally bound by the observed luminous matter in the clusters.
e. Galaxies appear dimmer than expected.