[单项选择]

You have been badly injured in a car accident. It is necessary to give you a blood transfusion(输血) because you lost a great deal of blood in the accident. However, special care must be taken in selecting new blood for you. If the blood is too different from your own, the transfusion could kill you.
There are four basic types of blood: A, B, AB and O. A simple test can indicate a person’ s blood type. Everybody is born with one of these four types of blood. Blood type, like hair color and height, is inherited from parents.
Because of substances contained in each type, the four groups must be transfused carefully. Basically, A and B cannot be mixed. A and B cannot receive AB, but AB may receive A or B. O can give to any other group; hence, it is often called the universal donor (通用献血者). For the opposite reason, AB is sometimes called universal recipient. However, because so many reactions can occur in transfusions, patients usually receive only salt or
A. the relationship between blood and nationality
B. trans fusion
C. human blood types
D. blood and gene