Given the task definition and input, reply with output. In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.

Article: Do you know blood types? Special care must be taken in selecting new blood for a badly injured person, who would be killed by the transfusion if the blood is too different from his own. There are four basic types of blood A. B. A B. and O. Blood type, like hair and height, comes from parents. Basically, A and B can not be mixed. AB, sometimes called the universal recipient , may receive A or B,. O type, often called the universal donor , gives his blood to any other group. Patients usually receive nothing, but salt or plasma until their blood can be matched as exactly as possible in the blood bank of a hospital. There is a relationship between your blood type and your nationality . Among Europeans, about 42 % have type A while 45 % have type O. The fewest is the type B.
Answer: as soon as accident happens
Usually person who has been injured and lost too much blood should be given a blood transfusion _ .