Astronomers Detect the Slight Anisotropy in the Cosmic Microwave Background

Multiple Choice

Astronomers detect the slight anisotropy in the cosmic microwave background by making redshift measurements: wavelengths coming from the direction of Aquarius are slightly longer and those from the direction of Leo are slightly shorter. This redshift is a

A) Doppler shift.
B) gravitational redshift.
C) cosmological redshift.
D) Doppler shift, gravitational redshift, or cosmological redshift since all three are one and the same thing.