Final answer:
Type B blood transfused into a person with type A blood causes a reaction between the donor's B antigen and the recipient's anti-B antibodies, leading to potentially dangerous agglutination.
Step-by-step explanation:
When type B blood is given to a person with type A blood, the B antigen from the donor reacts with the anti-B antibody in the recipient. This reaction can lead to agglutination (clumping of red blood cells), which can block blood vessels and cause serious complications. Therefore, the correct answer is 1) B antigen from the donor reacts with anti-B antibody in the recipient. This reaction can cause agglutination and hemolysis of the red blood cells, resulting in potentially life-threatening complications.