The Cosmological Redshift in the Light from Distant Galaxies Is

The cosmological redshift in the light from distant galaxies is explained by which effect?

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 we on Earth see 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 us and is therefore more gravitationally redshifted.