A difference between the A, B, and O blood types and the Rh factor is (a) Rh agglutinogens are not found on the surface of red blood cells, (b) Rh agglutinogens do not produce a cross-reaction, (c) individuals who are Rh− do not carry agglutinins to Rh factor unless they have been previously sensitized, (d) Rh agglutinogens are found free in the plasma, (e) Rh agglutinogens are found bound to plasma proteins.