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  3. What Is It? At the Center for Sickle-Cell Anemia in Benin City, Nigeria, Tope’ s mother learned that sickle-cell anemia is a

What Is It? At the Center for Sickle-Cell Anemia in Benin City, Nigeria, Tope’ s mother learned that sickle-cell anemia is a

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问题                          What Is It?
   At the Center for Sickle-Cell Anemia in Benin City, Nigeria, Tope’ s mother learned that sickle-cell anemia is a disorder of the blood. Contrary to superstitious beliefs, it has nothing to do with witchcraft or spirits of the dead. Children inherit sickle-cell anemia from both parents. It is not contagious. There is no way you can catch the disorder from another person. Either you are born with it or you are not. Tope’s mother also learned that while there is no cure, the symptoms can be treated.
   Sickle-cell anemia occurs mostly in those of African. descent. Dr. I. U. Omoike, director of the Center for Sickle-Cell Anemia, told Awake !: "Nigeria has the largest black population of any nation and therefore has the largest number of sicklers of any nation. That makes this country the sickle-cell capital of the world." According to the Daily Times of Lagos, about one million Nigerians have sickle-cell anemia, and 60,000 die of it each year.
A Problem in the Blood
   To understand the disorder, we need to know what blood does and how it moves through the body. An illustration helps. Imagine a country that depends on imported food to feed people living in rural villages. Trucks drive to the capital city where they are loaded with food. They leave the city along major highways, but as they enter the rural areas, the roads narrow.
   If everything goes well, the trucks reach their destination, drop off their food, and then return to the city to collect more food for the next delivery. If many of the trucks break down, however, the food spoils and other trucks are blocked from passing. Then the people in the villages have little to eat.
   In like manner, the red ceils in the blood travel to the lungs where they pick up a supply of oxygen-food for the body. They then leave the lungs and travel swiftly through major arteries to all parts of the body. Eventually, the "roads" become so small that the red cells can move only in single file through tiny blood vessels. It is there that they deposit their load of oxygen, which feeds the cells of the body.
   A normal red blood cell is round like a coin-and moves through the smallest blood vessels quite easily. But in people who have sickle-cell anemia, the blood cells break down. They lose their round shape and take the form of a banana or a sickle — a farmer’s implement. These sickled blood cells get stuck in the small veins of the body, like a truck in the mud, blocking other red blood cells from passing. When the flow of blood to a part of the body is reduced, the oxygen supply is cut off and the result is a painful crisis.
   A typical sickle-cell crisis results in cruciating pain in bones and joints.  Crises are unpredictable; they can occur rarely as often as every month. When they do occur, they are distressing to both child and parent. Ihunde is a nurse Who works at the sickle-cell center. "It is not easy to manage a sickler child," she says. "I know, because my daughter has the disorder. The pain comes suddenly. She screams and cries, and I cry. Only after two or three days, maybe after a week, will the pain subside."  
The terrible pain during a crisis is caused by______.
选项 A、the angular shape of the defective blood cells
B、the cutoff of oxygen supply in parts of the body
C、the cells stuck in the blood vessels
D、eating spoiled food
答案B
解析
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