B. Normal and moderate blood donation will not affect your health, but also help to improve the hematopoietic function of your own hematopoietic organs. Therefore, B is correct;
C, blood transfusion is based on the principle of blood transfusion of the same type. For example, in general, people with type A blood transfusion and people with type B blood transfusion. But in an emergency, if there is no blood of the same type, people of AB type can accept any blood type, but the blood transfusion should be slow and less. Type O blood can be transfused to people of any blood type, which is called universal blood transfusion. However, if a large number of O-type blood is transfused between different types, it may be very serious. "Universal blood transfusion" is not omnipotent, but also has potential dangers. According to the above introduction, we believe that except in special circumstances, O blood should not be lost to people of other blood types. We should insist on allogeneic blood transfusion as the most important basic principle in the field of blood transfusion, and C is correct;
D, blood transfusion should be based on the principle of blood transfusion with the same blood type, but in an emergency, people with AB blood type can accept any blood type, and O blood type can be lost to people with any blood type. Therefore, O-type blood can be exported to people with O-type blood as well as people with other blood types. It should be noted that if blood transfusion between people of different blood types is too fast and too much, the input lectin may also cause agglutination. Therefore, blood transfusion should be based on the principle of importing the same blood type.
Therefore, choose: d.