In the Figure Below, Three Identical Photons Were Each Emitted

Multiple Choice

In the figure below, three identical photons were each emitted when their local scale factor was R_U = 0.5.Each is then measured after the scale factor of the universe changes to a different amount, as shown.Which photon will be measured to have the greatest cosmological redshift?

A) the one at R_U =1
B) the one at R_U = 2
C) the one at R_U = 3
D) The photons at R_U = 2 and 3 will be identical, and have the greatest redshift.
E) All three will have the same cosmological redshift.