[单项选择]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.

[单项选择]Surveys indicate that 52 percent of all women aged eighteen to sixty-five are in the labor force (employed outside the home) in any given month. On the basis of these surveys, a market researcher concluded that 48 percent of all women aged eighteen to sixty-five are full-time homemakers year-round.
Which of the following, if true, would most seriously weaken the researcher’s conclusion
A. More women are in the labor force today than during any other period since the Second World War.
B. Many workers, both men and women, enter and exit the labor force frequently.
C. Although only a small sample of the total population is surveyed each month, these samples have been found to be a reliable indicator of total monthly employment.
D. Surveys show that more women than ever before consider having a rewarding job an important priority.
E. (E) Women who are in the labor force have more discretionary income available to them than do women who are not.

[单项选择]In a certain population, 40 percent of all people have biological characteristic X; the others do not. If 8,000 people have characteristic X, how many people do not have X ？（）
A. 3200
B. 4800
C. 12，000
D. 16，000
E. 20，000

[填空题]Fifty years ago, more than 75 percent of all adult women in the U.S. had no jobs.

[填空题]Eight percent of all the milk produced in the U.S. ends up in a frozen dairy product.

[单项选择]John D. Rockefeller,（），owned 90 percent of all American oil refineries.
A. as still a young man
B. while still a young man
C. a young man however
D. in spite of a young man

[单项选择]John D. Rockefeller, （）, owned 90 percent of all American oil refineries.
A. as still a young man
B. while still a young man
C. young man however
D. in spite a young man

[单项选择]Blood vessels running all through the lungs carry blood to each air sac (囊), or alveolus (肺泡), and then back again to the heart. Only the thin wall of the air sac and the thin wall of a capillary (毛细血管) are between the air and the blood. So oxygen easily diffuses from the air sacs through the walls into the blood, while carbon dioxide easily diffuses from the blood through the walls into the air sacs.
When blood is sent to the lungs by the heart, it has come back from the cells in the rest of the body. So the blood that goes into the wall of an air sac contains much dissolved carbon dioxide but very little oxygen. At the same time, the air that goes into the air sac contains much oxygen but very little carbon dioxide. You have learned that dissolved materials always diffuse from where there is more of them to where there is less. Oxygen from the air dissolves in the moisture on the lining of the air sac and diffuses through the lining into the blood. Meanwhile, carbon dioxide diff
A. inhaling some amount of oxygen
B. the evaporation of moisture
C. exhaling some amount of carbon dioxide
D. generating a passage for evaporation