When Hubble First Calculated the Recessional Speeds of Galaxies in the 1920s

Multiple Choice

When Hubble first calculated the recessional speeds of galaxies in the 1920s, he used

A) the Doppler shift relationship. This was an error, and the calculations had to be repeated using the cosmological redshift relationship.
B) the Doppler shift relationship. This was an error, and the calculations had to be repeated using the gravitational redshift relationship.
C) the Doppler shift relationship. This was correct because the nonrelativistic cosmological redshift relationship gives the same result.
D) the cosmological redshift relationship. This was an error, and the calculations had to be repeated using the Doppler shift relationship.