Explanation: Because your blood contains the A marker, it makes B antibodies. If B markers (found in type B or type AB blood) enter your body, your type A immune system gets fired up against them. This means that you can only get a transfusion from someone with A or O blood, not from someone with B or AB blood.
A person with type A blood cannot safely receive type B blood because the anti-B antibodies in the plasma of the type A recipient would bind to B antigens