D. Uracil which is what is use in RNa instead of thymine
The correct answer is D, white blood cells.
We know that red blood cells deliver nutrients and are not apart of the immune system; platelets are responsible for coagulation, which has nothing to do with the immune system, and plasma is a substance that, again, has nothing to do with immunity. White blood cells are the only things that fight disease (antibodies are white blood cells)!
I hope I helped!
(By nothing I meant very little to none).
