Correct Response: D. The Doppler effect causes light emitted by galaxies that are moving away from an observer to be shifted toward the red end of the spectrum. This is the same phenomenon that causes the sound produced by a receding ambulance siren to drop in frequency as its distance increases. The shift toward lower frequency wavelengths observed from galaxies that are moving away from Earth is greatest for galaxies that are the farthest from Earth. This shows that more distant galaxies are receding at a faster speed than galaxies that are closer to Earth. Since redshift by itself only provides evidence of a galaxy's rate of recession, it does not directly provide the location of galaxies (A) or information on their mass distribution and stage of development (B). Comparison of the redshifts of galaxies in different regions of space (C) has not provided evidence of galaxies clustered by age.
