The four blood types are【C1】______as A, B, AB, and O. Blood type A【C2】______red blood cell

s that have a substance A on their surface. This type of blood also contains an antibody directed【C3】______substance B, found on the red cells of persons with blood type【C4】______. Type B blood contains the【C5】______combination. Blood type AB contains【C6】______antibody, but red cells in this type of blood contain both A and B substances. In type O blood, neither substance is【C7】______on the red cells, but the individual is【C8】______of forming antibodies directed against red cells containing substance A or B. If blood type A is transfused【C9】______a person with B type blood, anti-A antibodies in the recipient will【C10】______the transfused A red cells. Because O type blood has【C11】______substance on its red cells, it can be given successfully【C12】______almost any person. Persons with blood type AB have no antibodies and can receive【C13】______of the four types of blood; thus blood types O and AB are called universal donors and universal recipients,【C14】______.

【C15】______hereditary blood-group systems have【C16】______been discovered. The hereditary blood constituent called Rh factor is of great【C17】______in blood transfusions because it creates reactions that can threaten the life of newborn【C18】______. More than twenty【C19】______blood types have been discovered. Their primary importance is in【C20】______cases involving proof of father-and-child relationship.

【C1】

A．called

B．named

C．known

D．recognized