Forty-five percent of all blood donated in the United States is type O. Type O blood is essential for emergencies where there is no time for determining the blood type of victims because type O blood can be used for everyone. Type O blood is unique in that it is compatible with blood of all types: any recipient, regardless of blood type, can be given it. But precisely because of this special usefulness, type O blood is chronically in short supply.
If the statements in the passage above are true, which of the following must also be true

A．The special usefulness of type O blood lies in the fact that it matches the blood type of most people.

B．Supplies of type O blood are continuously so low that type O blood is unavailable for emergencies, where its usefulness would be greatest.

C．Forty-five percent of the total population of the United State has type O blood, which makes type O the most common blood type.

D．Any decision to give blood of any type other than O needs to be based on knowledge of the recipient’s blood type.

E．(E) Type O blood is the only blood that cannot be typed as fast as needed in emergencies.