The Cosmological Redshift in the Light from Distant Galaxies Is

The cosmological redshift in the light from distant galaxies is explained by which of these effects?

A) A photon's wavelength is a distance and is therefore lengthened by the general expansion of the universe, making the light appear reddened.
B) The light observed on Earth was Doppler-shifted to longer wavelengths by the motion of the objects (e.g., galaxies) away from Earth.
C) The light spreads out over larger areas as distance increases according to 1/(distance) ², which causes the wavelength to increase in proportion to distance.
D) The light from more distant galaxies has traveled through the gravitational fields of more galaxies in getting to Earth and is therefore more gravitationally redshifted.