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The stratospheric ozone layer is not a completely uniform stratum, nor does it occur at the same altitude around the globe. It lies closest to the Earth over the poles and rises to maximum altitude over the equator. In the stratosphere, ozone is continuously being made and destroyed by natural processes. During the day the Sun breaks down some of the oxygen molecules to single oxygen atoms, and these reacting with the oxygen molecules that have not been dissociated, form ozone. However, the sunlight also breaks down ozone by converting some of it back to normal oxygen. In addition naturally occurring nitrogen oxides enter into the cycle and speed the breakdown reactions. The amount of ozone present at any one time is the balance between the processes that create it and those that destroy it.
Since the splitting of the oxygen molecules depends directly upon the intensity of solar radiation, the greatest rate of ozone production occurs over the tropics. However ozone is also destroyed most rapidly there, and wind circulation patterns carry the ozone-enriched upper layers of the atmosphere away from the equator. It turns out that the largest total ozone amounts are found at high latitudes. On a typical day the amount of ozone over Minnesota, for example, is 30 percent greater than the amount over Texas, 900 miles farther south. The density and altitude of the ozone layer also change with the seasons, the weather, and the amount of solar activity. Nevertheless, at any one place above the Earth’s surface, the long-term averages maintained by natural processes are believed to be reasonably constant.
The amount of ozone near the Earth is only a small percent of the amount in the stratosphere, and exchange of molecules between the ozone layer and the air at ground level is thought to be relatively small. Furthermore, the ozone molecule is so unstable that only a tiny fraction of ground-level ozone could survive the long trip to the stratosphere, so the ozone layer will not be replenished to any significant degree by the increasing concentrations of ozone that have been detected in recent years near the earth’s surface. The long-term averages of ozone both near ground level (ground level: n.[地质]地水准平面) and in the stratosphere are regulated by continuous processes that are constantly destroying and creating it in each of these places. This is why scientists are so concerned about human beings injection into the stratosphere of chemicals like nitrogen oxides, which are catalysts that facilitate the breakdown of ozone. If the ozone layer is depleted significantly, more ultraviolet radiation would penetrate to the Earth’s surface and damage many living organisms.
17. The passage suggests that factors contributing to the variation in the amount of ozone above different areas of the Earth’s surface include which of the following?
I. Some of the ozone found at higher latitudes was produced elsewhere.
II. There is usually a smaller amount of naturally occurring nitrogen oxide over high latitudes.
III. The rate of ozone production over the poles is less than that over the tropics.
(A) II only
(B) III only
(C) I and II only
(D) I and III only
(E) I, II, and III
18. Which of the following best states the central idea of the passage?
(A) Naturally occurring nitrogen oxides, as well as those introduced by humans, threaten to deplete the layer of ozone in the stratosphere.
(B) A delicate but reasonably constant balance exists between the natural processes that produce and those that destroy ozone in the stratosphere.
(C) There is little hope that the increased concentrations of ground-level ozone observed in recent years can offset any future depletion of stratospheric ozone.
(D) Meteorologically induced changes in the concentration of ozone in the stratosphere tend to cancel themselves out over a period of time.
(E) Solar radiation not only produces and destroys zone but also poses a hazard to human life.
19. The processes that determine the amount of ozone in a given portion of the stratosphere most resemble which of the following?
(A) Automobile emissions and seasonal fog that create a layer of smog over a city
(B) Planting and harvesting activities that produce a crop whose size is always about the same
(C) Withdrawals and deposits made in a bank account whose average balance remains about the same
(D) Assets and liabilities that determine the net worth of a corporation
(E) High grades and low grades made by a student whose average remains about the same from term to term
20. According to the passage, which of the following has the LEAST effect on the amount of ozone at a given location in the upper atmosphere?
(A) Latitude
(B) Weather
(C) Season
(D) Ground-level ozone
(E) Solar activity
21. The author provides information that answers which of the following questions?
I. What is the average thickness of the stratospheric ozone layer?
II. Why does increased exposure to ultraviolet radiation damage many living organisms?
III. What is the role of oxygen in the production of stratospheric zone?
(A) I only
(B) II only
(C) III only
(D) I and II
(E) II and III
22. In explaining what determines the amount of ozone in the stratosphere, the author describes natural processes that form
(A) an interactive relationship
(B) a reductive system
(C) a linear progression
(D) a set of randomly occurring phenomena
(E) a set of sporadically recurring events
Feelings of hopelessness among medieval workers trapped in the poverty cycle gradually lessened as it became possible for women’s labor to supplement a family’s money income by more than pennies. By 1300, women spinners could be found working on their own (on one's own: adv.独自地, 独立地, 主动地) for wealthy sponsors, even after the introduction in Italy and France of prohibition against advancing money for supplies to women spinners. Historians have usually interpreted this prohibition simply as evidence of women’s economic subjection, since it obliged them to turn to usurers; however, it was also almost certainly a response to a trend toward differential reward for women’s higher skill. Yarn can be spun irregularly and lumpily, but perfectly smooth yarn is worth more. Working for merchant entrepreneurs on time rates, women had been paid hardly more than children; working as entrepreneurs themselves and producing good work by the piece, they could break into (to make entry or entrance into “broke into the house” “break into show business”) the rational system of differential rewards.
23. The primary purpose of the passage is to
(A) propose and defend a theory about the consequences of a certain historical event
(B) present historical facts and offer a broader interpretation of those facts than has been offered in the past
(C) describe the socioeconomic effects of a widely held attitude during a particular historical period
(D) demonstrate the superiority of using an economic approach to historical analysis
(E) call attention to the influence of the textile industry on society during a particular historical period
24. It can be inferred from the passage that the author views the system of paying all workers equally on time rates as
(A) unfair and not rational
(B) undesirable but unavoidable
(C) efficient and profitable
(D) advantageous to most women workers
(E) evidence of a trend toward a more modern wage system
25. The passage implies which of the following about women spinners in medieval Europe?
(A) Most of them worked independently for wealthy sponsors.
(B) They were not typical of medieval women entrepreneurs.
(C) Some of them were paid for their work after it was done, according to its value.
(D) They would have been able to contribute substantial amounts to their families incomes were it not for the prohibition against advancing money to them.
(E) They were inevitably disadvantaged in the marketplace because they were obliged to obtain money for their supplies from usurers.
26. The passage implies that feelings of hopelessness among medieval workers
(A) resulted primarily from the lack of a rational system of differential rewards
(B) disappeared completely once medieval textile workers were able to break the cycle of poverty
(C) were more prevalent among female workers than among male workers
(D) came into being in part because of women’s limited earning capacity
(E) were particularly common among textile workers in Italy and France
27. The author suggests that historians have done which of the following?
(A) Failed to give adequate consideration to the economic contribution of women during the medieval period.
(B) Overestimated the degree of hopelessness experienced by medieval workers trapped in the poverty cycle.
(C) Ignored the fact that by 1300 many women spinners were working independently rather than for merchant entrepreneurs.
(D) Regard the economic status of women in Italy and France as representative of women’s status throughout medieval Europe.
(E) Overlooked part of the significance of a prohibition governing one aspect of yarn production in medieval Europe.
答案：17-27：DBCDCABACDE
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