What Is the "Cosmological Redshift

Multiple Choice

What is the "cosmological redshift"?

A) stretching of the wavelengths of photons as they travel through expanding space
B) stretching of the wavelengths of photons by the Doppler shift because they are emitted by galaxies that are moving away from Earth
C) loss of energy from photons interacting with virtual particles in the vacuum, resulting in the wavelength of the photons gradually increasing as they travel toward Earth through space
D) stretching of the wavelengths of photons as they pass through absorbing matter in galaxies between Earth and the emitting galaxy