Science Test - Continues

This question refers to the passage and the chart.

In the ABO blood group system, the primary human blood types are A, B, AB, and O. The letters refer to proteins on the surfaces of red blood cells called antigens. These antigens can provoke an immune response. The liquid part of blood, called plasma, contains antibodies against antigens that are not on a person's red blood cells. For example, a person with type B blood makes anti-A antibodies, which attack any blood cell with an A antigen on it. If a person is given a blood transfusion of an incompatible type, the person's blood cells will clump together and block blood flow, which can lead to death. A blood type with no antigens on the red blood cells is called a universal donor because all other blood types can receive this blood type through transfusions.

Which answer choice represents the universal blood donor(s)?

^1. A only

^2. B and O

^3. O only

^4. AB only

^5. A and B

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