The correct answer is: O-
Blood type is determined by the presence or absence of certain antigens on the surface of red blood cells. There are four main blood types: A, B, AB, and O. Blood type is also classified as Rh positive or Rh negative, depending on the presence or absence of the Rh antigen.
O- blood is called the universal donor because it can be donated to people with any blood type. This is because O- blood does not have any antigens on the surface of red blood cells. People with O- blood are called universal donors because their blood can be safely transfused to people with any blood type.
A- blood can only be donated to people with A or AB blood. B- blood can only be donated to people with B or AB blood. AB+ blood can be donated to people with A, B, AB, or O blood. AB- blood is the rarest blood type and can only be donated to people with AB- blood.
It is important to note that blood type is not the only factor that determines whether or not a blood transfusion is safe. The Rh factor, blood type antibodies, and the patient’s medical condition must also be considered.