Which statement about type O blood is true?

• A. It has surface antigens A and B
• B. It has anti-A antibodies only
• C. Lacks both A and B antigens and has both anti-A and anti-B antibodies
• D. It has surface antigen A

Answer: (C)

The key idea is how the ABO system is organized: red blood cells show certain surface antigens, and plasma contains antibodies against the antigens a person does not have. Type O blood has no A or B antigens on the red cells, and its plasma contains antibodies against both A and B. That combination is why the true statement says it lacks both A and B antigens and has anti-A and anti-B antibodies. If a person with type O received blood with A or B antigens, their antibodies could attack those antigens. Conversely, other options would imply the presence of A or B antigens or missing antibodies, which doesn’t describe type O.