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10.(Z14)In each of the past five years, Barraland’s prison population has increased.  Yet, according to official government statistics, for none of those years has there been either an increase in the number of criminal cases brought to trial, or an increase in the rate at which convictions have been obtained.  Clearly, therefore, the percentage of people convicted of crimes who are being given prison sentences is on the increase.

Which of the following, if true, most seriously weakens the argument?

A.        In Barraland the range of punishments that can be imposed instead of a prison sentence is wide.
B.        Over the last ten years, overcrowding in the prisons of Barraland has essentially been eliminated as a result of an ambitious program of prison construction.
C.        Ten years ago, Barraland reformed its criminal justice system, imposing longer minimum sentences for those crimes for which a prison sentence had long been mandatory.
D.        Barraland has been supervising convicts on parole more closely in recent years, with the result that parole violations have become significantly less frequent.
E.        The number of people in Barraland who feel that crime is on the increase is significantly greater now than it was five years ago.

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9.(Z14)Eurasian watermilfoil, a weed not native to Frida Lake, has reproduced prolifically since being accidentally introduced there.  In order to eliminate the weed, biologists proposed treating infested parts of the lake with a certain herbicide that is nontoxic for humans and aquatic animals.  However, the herbicide might damage populations of certain rare plant species that the lake contains.  For this reason local officials rejected the proposal.

Which of the following, if true, points out the most serious weakness in the officials’ grounds for rejecting the biologists’ proposal?

A.        The continuing spread of Eurasian watermilfoil in Frida Lake threatens to choke out the lake’s rare plant species.
B.        Because of ecological conditions prevailing in its native habitat, Eurasian watermilfoil is not as dominant there as it is in Frida Lake.
C.        The proliferation of Eurasian watermilfoil in Frida Lake has led to reductions in the populations of some species of aquatic animals.
D.        Although Eurasian watermilfoil could be mechanically removed from Frida Lake, eliminating the weed would take far longer this way than it would using herbicides.
E.        Unless Eurasian watermilfoil is completely eliminated from Frida Lake, it will quickly spread again once herbicide treatments or other control measures cease.

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8.(Z)In 1983 Argonia’s currency, the argon, underwent a reduction in value relative to the world’s strongest currencies. This reduction resulted in a significant increase in Argonia’s exports over 1982 levels. In 1987 a similar reduction in the value of the argon led to another increase in Argonia’s exports. Faced with the need to increase exports yet again, Argonia’s finance minister has proposed another reduction in the value of the argon.

Which of the following, if true, most strongly supports the prediction that the finance minister’s plan will not result in a significant increase in Argonia’s exports next year?
A.        The value of the argon rose sharply last year against the world’s strongest currencies.
B.        In 1988 the argon lost a small amount of its value, and Aronian exports rose slightly in 1989.
C.        The value of Argonia’s exports was lower last year than it was the year before.
D.        All of Argonia’s export products are made by factories that were operating at full capacity last year, and new factories would take years to build.
E.        Reductions in the value of the argon have almost always led to significant reductions in the amount of goods and services that Argonians purchase from abroad.

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7.(Z10)Certain genetically modified strains of maize produce a natural insecticide that protects against maize-eating insects.  The insecticide occurs throughout the plant, including its pollen.  Maize pollen is dispersed by the wind and often blows onto milkweed plants that grow near maize fields.  Caterpillars of monarch butterflies feed exclusively on milkweed leaves.  When, in experiments, these caterpillars were fed milkweed leaves dusted with pollen from modified maize plants, they died.  Therefore, use of the modified maize inadvertently imperils monarch butterflies.

Which of the following, if true, most seriously weakens the argument?

A.        Per unit of volume, the natural insecticide produced by the genetically modified maize plants is less toxic to insects than are many commercial insecticides commonly used on maize plants.
B.        Standard weed-control practices that have been used by farmers for decades have largely eliminated milkweed plants from certain areas where monarch-butterfly caterpillars were once common.
C.        The experiments showed that the caterpillars were not harmed by contact with the pollen from the genetically modified plants unless they ingested it.
D.        The maize-eating insects that the natural insecticide protects against do not feed on the pollen of the maize plant.
E.        Airborne maize pollen tends to collect on the middle leaves of milkweed plants and monarch caterpillars feed only on the plant’s tender upper leaves.

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6.(Z13)FastMart, a convenience store chain, is planning to add pancake syrup to the items it sells.  FastMart stores do not have shelf space to stock more than one variety of syrup.  Surveys of FastMart customers indicate that one-fourth of them prefer low-calorie syrup, while three-fourths prefer regular syrup.  Since FastMart’s highest priority is to maximize sales, the obvious strategy for it is to stock regular syrup.

Which of the following, if true, most seriously weakens the argument?

A:        People buying pancake syrup at convenience stores, unlike those buying it at supermarkets, generally buy it only a few times.
B.        People who prefer low-calorie syrup generally use about the same amount of syrup on their pancakes as those who prefer regular syrup.
C.        Regular syrup does not sell for a higher price per unit than low-calorie syrup.
D.        In general, customers who prefer regular syrup will buy low-calorie syrup if regular is unavailable, but those who prefer low-calorie will not buy regular syrup.
E.        Sales of syrup are not expected to account for a large proportion of total dollar sales at the average FastMart store.

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5.(Z5)Insect infestations in certain cotton-growing regions of the world have caused dramatic increase in the price of cotton on the world market. By contrast, the price of soybeans has long remained stable. Knowing that cotton plants mature quickly, many soybean growers in Ortovia plan to cease growing soybeans and being raising cotton instead, thereby taking advantage of the high price of cotton to increase their income significantly, at least over the next several years.

Which of the following, if true, most seriously weakens the plan’s chances for success?

A.        The cost of raising soybeans has increased significantly over the past several year and is expected to continue to climb.
B.        Tests of a newly developed, inexpensive pesticide have shown it to be both environmentally safe and effective against the insects that have infested cotton crops.
C.        In the past several years, there has been no sharp increase in the demand for cotton and for goods made out of cotton.
D.        Few consumers would be willing to pay significantly higher prices for cotton goods than they are now paying.
E.        The species of insect that has infested cotton plants has never been known to attack soybean plants.

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4.(Z4)It is theoretically possible that bacteria developed on Mars early in its history and that some were carried to Earth by a meteorite.  However, strains of bacteria from different planets would probably have substantial differences in protein structure that would persist over time, and no two bacterial strains on Earth are different enough to have arisen on different planets.  So, even if bacteria did arrive on Earth from Mars, they must have died out.

The argument is most vulnerable to which of the following criticisms?

A.        It fails to establish whether bacteria actually developed on Mars.
B.        It fails to establish how likely it is that Martian bacteria were transported to Earth.
C.        It fails to consider whether there were means other than meteorites by which Martian bacteria could have been carried to Earth.
D.        It fails to consider whether all bacteria now on Earth could have arisen from transported Martian bacteria.
E.        It fails to consider whether there could have been strains of bacteria that originated on Earth and later died out.

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3.（Z4）Proposal:  Carbon dioxide and methane in the atmosphere block the escape of heat into space.  So emission of these “greenhouse” gases contributes to global warming.  In order to reduce global warming, emission of greenhouse gases needs to be reduced.  Therefore, the methane now emitted from open landfills should instead be burned to produce electricity.

Objection:  The burning of methane generates carbon dioxide that is released into the atmosphere.

Which of the following, if true, most adequately counters the objection made to the proposal?

A.        Every time a human being or other mammal exhales, there is some carbon dioxide released into the air.
B.        The conversion of methane to electricity would occur at a considerable distance from the landfills.
C.        The methane that is used to generate electricity would generally be used as a substitute for a fuel that does not produce any greenhouse gases when burned.
D.        Methane in the atmosphere is more effective in blocking the escape of heat from the Earth than is carbon dioxide.
E.        The amount of methane emitted from the landfills could be reduced if the materials whose decomposition produces methane were not discarded, but recycled.

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2.(Z3)Kate:  The recent decline in numbers of the Tennessee warbler, a North American songbird that migrates each fall to coffee plantations in South America, is due to the elimination of the dense tree cover that formerly was a feature of most South American coffee plantations.

Scott:  The population of the spruce budworm, the warbler’s favorite prey in North America, has been dropping.  This is a more likely explanation of the warbler’s decline.

Which of the following, if true, most seriously calls Scott’s hypothesis into question?

A.        The numbers of the Baltimore oriole, a songbird that dose not eat budworms but is as dependent on South American coffee plantations as is the Tennessee warbler, are declining.
B.        The spruce-budworm population has dropped because of a disease that can infect budworms but not Tennessee warblers.
C.        The drop in the population of the spruce budworm is expected to be only temporary.
D.        Many Tennessee warbler have begun migrating in the fall to places other than traditional coffee plantations.
E.        Although many North American songbirds have declined in numbers, no other species has experienced as great a decline as has the Tennessee warbler.

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练习题：
1.（Z1-13）In the United States, of the people who moved from one state to another when they retired, the percentage who retired to Florida has decreased by three percentage points over the past ten years.  Since many local businesses in Florida cater to retirees, this decline is likely to have a noticeably negative economic effect on these businesses.

Which of the following, if true, most seriously weakens the argument?

A. Florida attracts more people who move from one state to another when they retire than does any other state.
B. The number of people who move out of Florida to accept employment in other states has increased over the past ten years.
C. There are far more local businesses in Florida that cater to tourists than there are local businesses that cater to retirees.
D. The total number of people who retired and moved to another state for their retirement has increased significantly over the past ten years.
E. The number of people who left Florida when they retired to live in another state was greater last year than it was ten years ago.