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2. Defense department analysts worry that the ability of the United States to wage a prolonged war would be seriously endangered if the machine-tool manufacturing base shrinks further. Before the Defense Department publicly connected this security issue with the import quota issue, however, the machine-tool industry raised the national security issue in its petition for import quotas.

Which of the following, if true, contributes most to an explanation of the machine-tool industry’s raising the issue above regarding national security?

A. When the aircraft industries retooled, they provided a large amount of work for too builders.
B. The Defense Department is only marginally concerned with the effects of foreign competition on the machine-tool industry.
C. The machine-tool industry encountered difficulty in obtaining governmental protection against imports on grounds other than defense.
D. A few weapons important for defense consist of parts that do not require extensive machining.
E. Several federal government programs have been designed which will enable domestic machine-tool manufacturing firms to compete successfully with foreign toolmakers.

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3. In Asia, where palm trees are non-native, the trees’ flowers have traditionally been pollinated by hand, which has kept palm fruit productivity unnaturally low. When weevils known to be efficient pollinators of palm flowers were introduced into Asia in 1980, palm fruit productivity increased-by up to fifty percent in some areas-but then decreased sharply in 1984.

Which of the following statements, if true, would best explain the 1984 decrease in productivity?

A. Prices for palm fruit fell between 1980 and 1984 following the rise in production and a concurrent fall in demand.
B. Imported trees are often more productive than native trees because the imported ones have left behind their pests and diseases in their native lands.
C. Rapid increases in productivity tend to deplete trees of nutrients needed for the development of the fruit-producing female flowers.
D. The weevil population in Asia remained at approximately the same level between 1980 and 1984. C
E. Prior to 1980 another species of insect pollinated the Asian palm trees, but not as efficiently as the species of weevil that was introduced in 1980.

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4. The tobacco industry is still profitable and projections are that it will remain so. In the United States this year, the total amount of tobacco sold by tobacco-farmers has increased, even though the number of adults who smoke has decreased.

Each of the following, if true, could explain the simultaneous increase in tobacco sales and decrease in the number of adults who smoke EXCEPT:
A. During this year, the number of women who have begun to smoke is greater than the number of men who have quit smoking
B. The number of teen-age children who have begun to smoke this year is greater than the number of adults who have quit smoking during the same period
C. During this year, the number of nonsmokers who have begun to use chewing tobacco or snuff is greater than the number of people who have quit smoking
D. The people who have continued to smoke consume more tobacco per person than they did in the past
E. More of the cigarettes made in the United States this year were exported to other countries than was the case last year.

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5. Extinction is a process that can depend on a variety of ecological, geographical, and physiological variables. These variables affect different species of organisms in different ways, and should, therefore, yield a random pattern of extinctions. However, the fossil record shows that extinction occurs in a surprisingly definite pattern, with many species vanishing at the same time.

Which of the following, if true, forms the best basis for at least a partial explanation of the patterned extinctions revealed by the fossil record?

(A) Major episodes of extinction can result from widespread environmental disturbances that affect numerous different species.
(B) Certain extinction episodes selectively affect organisms with particular sets of characteristics unique to their species.
(C) Some species become extinct because of accumulated gradual changes in their local environments.
(D) In geologically recent times, for which there is no fossil record, human intervention has changed the pattern of extinctions.
(E) Species that are widely dispersed are the least likely to become extinct.

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6.(Z)When a new restaurant, Martin’s Cafe, opened in Riverville last year, many people predicted that business at the Wildflower Inn, Riverville’s only other restaurant, would suffer from the competition.  Surprisingly, however, in the year since Martin’s Cafe opened, the average number of meals per night served at the Wildflower Inn has increased significantly.
Which of the following, if true, most helps to explain the increase?

A.        Unlike the Wildflower Inn, Martin’s Cafe serves considerably more meals on weekends than it does on weekdays.
B.        Most of the customers of Martin’s Cafe had never dined in Riverville before this restaurant opened, and on most days Martin’s Cafe attracts more customers than it can seat.[/b]
C.        The profit per meal is higher, on average, for meals served at Martin’s Cafe than for those served at the Wildflower Inn.
D.        The Wildflower Inn is not open on Sundays, and therefore Riverville residents who choose to dine out on that day must either eat at Martin’s Cafe or go to neighboring towns to eat.
E.        A significant proportion of the staff at Martin’s Cafe are people who formerly worked at the Wildflower Inn and were hired away by the owner of Martin’s Cafe.

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7.(Z)Maize contains the vitamin niacin, but not in a form the body can absorb.  Pellagra is a disease that results from niacin deficiency.  When maize was introduced into southern Europe from the Americas in the eighteenth century, it quickly became a dietary staple, and many Europeans who came to subsist primarily on maize developed pellagra.  Pellagra was virtually unknown at that time in the Americas, however, even among people who subsisted primarily on maize.

Which of the following, if true, most helps to explain the contrasting incidence of pellagra described above?

A.        Once introduced into southern Europe, maize became popular with landowners because of its high yields relative to other cereal crops.
B.        Maize grown in the Americas contained more niacin than maize grown in Europe did.
C.        Traditional ways of preparing maize in the Americas convert maize’s niacin into a nutritionally useful form.
D.        In southern Europe many of the people who consumed maize also ate niacin-rich foods.
E.        Before the discovery of pellagra’s link with niacin, it was widely believed that the disease was an infection that could be transmitted from person to person.

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8.(Z)Wolves generally avoid human settlements.  For this reason, domestic sheep, though essentially easy prey for wolves, are not usually attacked by them.  In Hylantia prior to 1910, farmers nevertheless lost considerable numbers of sheep to wolves each year.  Attributing this to the large number for wolves, in 1910 the government began offering rewards to hunters for killing wolves.  From 1910 to 1915, large numbers of wolves were killed.  Yet wolf attacks on sheep increased significantly.

Which of the following, if true, most helps to explain the increase in wolf attacks on sheep?

A.        Populations of deer and other wild animals that wolves typically prey on increased significantly in numbers from 1910 to 1915.
B.        Prior to 1910, there were no legal restrictions in Hylantia on the hunting of wolves.
C.        After 1910 hunters shot and wounded a substantial number of wolves, thereby greatly diminishing these wolves’ ability to prey on wild animals.
D.        Domestic sheep are significantly less able than most wild animals to defend themselves against wolf attacks.
E.        The systematic hunting of wolves encouraged by the program drove many wolves in Hylantia to migrate to remote mountain areas uninhabited by humans.

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9.(Z)Nitrogen dioxide is a pollutant emitted by automobiles.  Catalytic converters, devices designed to reduce nitrogen dioxide emissions, have been required in all new cars in Donia since 1993, and as a result, nitrogen dioxide emissions have been significantly reduced throughout most of the country.  Yet although the proportion of new cars in Donia’s capital city has always been comparatively high, nitrogen dioxide emissions there have showed only an insignificant decline since 1993.

Which of the following, if true, most helps to explain the insignificant decline in nitrogen dioxide emissions in Donia’s capital city?

A.        More of the cars in Donia’s capital city were made before 1993 than after 1993.
B.        The number of new cars sold per year in Donia has declined slightly since 1993.
C.        Pollutants other than nitrogen dioxide that are emitted by automobiles have also been significantly reduced in Donia since 1993.
D.        Many Donians who own cars made before 1993 have had catalytic converters installed in their cars.
E.        Most car trips in Donia’s capital city are too short for the catalytic converter to reach its effective working temperature.

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10.(Z)Escalating worldwide demand for corn has led to a sharp increase in the market price of corn, and corn prices are likely to remain high.  Corn is extensive used as feed for livestock, and because profit margins are tight in the livestock business, many farmers are expected to leave the business.  With fewer suppliers, meat prices will surely rise.  Nonetheless, observers expect an immediate short-term decrease in meat prices.

Which of the following, if true, most helps to justify the observers’ expectation?

A.        The increase in corn prices is due more to a decline in the supply of corn than to a growth in demand for it.
B.        Generally, farmers who are squeezed out of the livestock business send their livestock to market much earlier than they otherwise would.
C.        Some people who ate meat regularly in the past are converting to diets that include little or no meat.
D.        As meat prices rise, the number of livestock producers is likely to rise again.
E.        Livestock producers who stay in the business will start using feed other than corn more extensively than they did in the past.

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练习题：
1. (Z)In order to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the sand. Such burrowing discourages barnacles from clinging to their shells. When fully grown, however, the crabs can readily withstand tidal currents without burrowing, and thus they acquire substantial populations of barnacles. Surprisingly, in areas where tidal currents are very weak, juvenile horseshoe crabs are found not to have significant barnacle populations, even though they seldom burrow.

Which of the following, if true, most helps to explain the surprising finding?

A.        Tidal currents do not themselves dislodge barnacles from the shells of horseshoe crabs.
B.        Barnacles most readily attach themselves to horseshoe crabs in areas where tidal currents are weakest.
C.        The strength of the tidal currents in a given location varies widely over the course of a day.
D.        A very large barnacle population can significantly decrease the ability of a horseshoe crab to find food.
E.        Until they are fully grown, horseshoe crabs shed their shells and grow new ones several times a year.