Why Do We See a Gravitational Redshift in the Spectrum

Multiple Choice

Why do we see a gravitational redshift in the spectrum of the Sun?

A) Gravity makes light heavy,causing it to appear redder.
B) Because of gravity,the Sun is always moving away from us,so we see a redshift.
C) Time runs slower on the Sun than on Earth,making lines in the solar spectrum have lower frequency and hence longer wavelength than normal.
D) Spacetime curvature allows red photons of light to escape the Sun more easily than blue photons,leading to an apparent redshift.