What Is the Primary Practical Difficulty That Limits the Use

Multiple Choice

What is the primary practical difficulty that limits the use of Hubble's law for measuring distances?

A) Redshifts of galaxies are difficult to measure.
B) The recession velocities of distant galaxies are so great that they are hard to measure.
C) We do not know Hubble's constant very accurately yet.
D) Hubble's law is only useful theoretically;it is difficult to use in practice.
E) The motion of Earth relative to the Milky Way is difficult to account for.