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  3. "Ouch!" you cry as your doctor "stabs" you in a finger or in that sensitive spot on the inside of your elbow opposite your elbow

"Ouch!" you cry as your doctor "stabs" you in a finger or in that sensitive spot on the inside of your elbow opposite your elbow

admin2009-04-27  81
问题     "Ouch!" you cry as your doctor "stabs" you in a finger or in that sensitive spot on the inside of your elbow opposite your elbow. "Is the sharp, if momentary, pain necessary?" You wonder as the doctor takes a sample of your blood. What is she up to anyway? What are blood tests for?
    Your blood is a vital part of your body. It picks up oxygen in your lungs and carries it to your cells, which use the oxygen to produce energy. It carries wastes away from your cells. It carries white blood cells and disease-fighting chemicals called antibodies to places where foreign invaders such as bacteria and viruses are causing infections. The white blood cells gobble up the invaders, and the antibodies knock them out.
    Your blood also carries food from your stomach and small intestine to all parts of your body. Clearly, a large loss of blood from an accident or disease can have serious consequences.
    So can an imbalance of the blood’s parts. For example, a low concentration of white cells reduces the body’s ability to fight infection. A low concentration of oxygen-carrying red cells robs the body of energy releasing oxygen.
    Suppose you lost a lot of blood, what would a doctor do? Replace the blood quickly as possible by giving you a transfusion of blood donated by another person. But the doctor can’t use just anyone’s blood. The donor’s blood has to be of a type that won’t be destroyed by your blood. Blood type? What’s that?
    Remember the blood your doctor took from you? Well, some of that blood may have been used to find your blood type—A, B, AB, or O. Each of us has one of these basic blood types (plus a number of subtypes). People with a certain type can receive blood of only certain other types.
    To find your blood type, the doctor sends your blood to a laboratory. There your red cells are separated from the other parts of your blood. These cells may have certain antigens (special proteins) on their surfaces—"A" antigens and/or "B" antigens. If your red cells have "A" antigens you are type A, "B" antigens make you type B both "A" and "B" antigens make you type AB, neither "A" nor "B" antigens makes you type O. How do you find those antigens?
    A lab technician mixes your red blood cells with two kinds of blood serum. One contains anti-A antibodies. The other kind contains anti-B antibodies. An antibody is a substance that "attacks" a particular antigen, in this case "A" or "B" antigens.
    The technician taken looks at each mixture under a microscope to see what will happen to your blood cells. Certain mixtures may make your red cells clump together. By finding which mixtures do this and which do not, the technician can figure out your blood type.
    But blood typing isn’t the only reason to have a blood test taken. It can also check for signs of infection. How? When you have an infection, especially a serious one, the number of white blood cells soars. This is normal response of your body to an invasion of germs.
    This time, a sample of blood goes to the lab for a CBC—complete blood count. A technician will examine your blood under a microscope—counting the white cells in a small marked-off area. If the number is much higher than it ought to be, the doctor may need to treat you to be sure the infection doesn’t spread.
    Other blood tests can determine the concentration of various chemicals in your blood or the variety and types of blood cells circulating in the blood. The information hidden in a drop of blood may lead a doctor to suggest ways to treat. Or avoid dangerous health conditions.
    Was the stick in the finger or arm necessary? If protecting yourself from danger is necessary, the answer has got to be—yes!
选项 A、proves how blood fights against invaders
B、implies how invaders cause infections
C、dose not tell how white cells fight against foreign invaders
D、explain the functions of the red cells and white cells
答案C
解析 单句释义题。该句的下句只提到白血球贪婪地吞噬侵入的异物，而抗体则把它们摧毁，可见文中并未提到白血球如何与入侵异物抗争。
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