What phenomenon was discovered by early astronomers and used by Hubble to confirm that the universe is expanding? A. The light emitted by the galaxies becomes brighter as they move away from one another
.B. The light emitted by the galaxies becomes whiter as they move away from one another.
C. The wavelength of the light emitted by the galaxies shifts to the blue region of the spectrum as the galaxies move away from one another.
D. The wavelength of the light emitted by the galaxies shifts to the red region of the spectrum as the galaxies move away from one another.