different sizes of red blood cells different sizes of white blood cells different marker proteins on red blood cells different marker proteins on white blood cells
I gave my students this multiple choice question: How do blood types differ from one another in the ABO blood classification?

Only one answer is correct among these 4 choices:
- different sizes of red blood cells
- different sizes of white blood cells
- different marker proteins on red blood cells
- different marker proteins on white blood cells

Could you tell me which one is correct?

different marker proteins on red blood cells