If a patient with blood group B requires an immediate blood transfusion, this type can be given

The correct option is B and O.

To understand why a patient with blood group B can safely receive blood from donors with blood groups B and O, we must look at the antigens and antibodies involved in the ABO blood group system:
1. Recipient's Blood Group (Group B): A person with blood group B has B antigens on the surface of their red blood cells and produces anti-A antibodies in their blood plasma.
2. Immune Response Rule: During a blood transfusion, the recipient's antibodies must not recognize the donor's red blood cell antigens as foreign. If they do, the recipient's antibodies will attack the donor cells, causing a life-threatening reaction (agglutination and hemolysis).
3. Donor Group B: Donor red blood cells have B antigens. Since the recipient has blood group B, their immune system recognizes B antigens as self and will not attack them. Therefore, group B blood is compatible.
4. Donor Group O: Donor red blood cells in group O have no A or B antigens on their surface. Because there are no antigens for the recipient's anti-A antibodies to bind to, group O blood can be safely transfused. This is why group O is known as the universal donor.
5. Incompatible Groups (A and AB): Blood groups A and AB both contain A antigens. If transfused, the recipient's anti-A antibodies would immediately bind to and destroy these cells, making them unsafe for a group B recipient.