What Tissue Would Provide Evidence for the Increased Production of Red

What tissue would provide evidence for the increased production of red blood cells following doping with erythropoietin?

A) in the lungs of the individual
B) Increased red blood cells would be found in the kidneys because that is the site of natural erythropoietin.
C) The increase in red blood cells would be most obvious in the arterial blood supply and not the venous supply.
D) In the bone marrow there would be an increase in the number of immature red blood cells being produced.
E) There is no source of red blood cells to look at for a change in production.