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Ed, who has blood type AB+, needs a blood transfusion. He can get the blood from Sally who is O- or from Bob, who is A+. Which blood type would cause the least reaction from his body and why.
Bob's blood would cause the least reaction. In this blood are also anti-B antibodies, that may start to attack some of his blood cells.
However, Sally's blood, O-, contains anti-bodies to A and B, and possible the Rh factor. So her blood contains more anti-bodies that could attack Bob's own blood cells.