Spectral Lines Detected from the Surfaces of White Dwarf Stars

Spectral lines detected from the surfaces of white dwarf stars are slightly redshifted with respect to the equivalent spectral absorption lines in the laboratory. Why is this?

A) The rapid rotation of these stars produces a redshift of light from atoms on their surfaces.
B) The extremely high temperature of the star surface affects the atomic energy levels and therefore the spectral lines produced by the atoms.
C) The steady shrinkage of white dwarf stars as they evolve is reflected in Doppler redshift of the surface spectrum.
D) Photons are gravitationally redshifted by the intense gravity field of the star.