Critical Reasoning

Charcoal from a hearth site in Colorado, 2,000 miles south of Alaska, is known to be 11,200 years old. Siberia is located in northeast Russia, and Alaska is located in northwest America. Researchers reasoned since glaciers prevented human migration south from the Alaska-Siberia land bridge between 18,000 and 11,000 years ago, humans must have come to the Americas more than 18,000 years ago. Which of the following pieces of new evidence would cast doubt on the conclusion drawn above?

A group of children of various ages was read stories in which people caused harm, with some of those people doing so intentionally and some accidentally. When asked about appropriate punishments for those who had caused harm, the younger children, unlike the older ones, assigned punishments that did not vary according to whether the harm was done intentionally or accidentally. Younger children, then, do not regard people’s intentions as relevant to punishment. Which of the following, if true, would most seriously weaken the conclusion above?

Mansour: We should both plan to change some of our investments from coal companies to less polluting energy companies, and here’s why: Consumers are increasingly demanding nonpolluting energy, and energy companies are increasingly supplying it. Therese: I’m not sure we should do what you suggest. As demand for nonpolluting energy increases relative to supply, its price will increase, and then the more polluting energy will cost relatively less. Demand for the cheaper, dirtier energy forms will then increase, as will the stock values of the companies that produce them. Therese responds to Mansour’s proposal by doing which of the following?

The earliest Mayan pottery found at Colha in Belize is about 3,000 years old. Recently, however, 4,500-year-old stone agricultural implements were unearthed at Colha. These implements resemble Mayan stone implements of a much later period, also found at Colha. Moreover, the implements’ designs are strikingly different from the designs of stone implements produced by other cultures known to have inhabited the area in prehistoric times. Therefore, there were surely Mayan settlements in Colha 4,500 years ago. Which of the following, if true, most seriously weakens the argument?

Duckbill dinosaurs, like today’s monitor lizards, had particularly long tails, which they could whip at considerable speed. Monitor lizards use their tails to strike predators. However, although duckbill tails were otherwise very similar to those of monitor lizards, the duckbill’s tailbones were proportionately much thinner and thus more delicate. Moreover, to ward off their proportionately much larger predators, duckbills would have had to whip their tails considerably faster than monitor lizards do. The information given, if accurate, provides the strongest support for which of the following hypotheses?

In an attempt to produce a coffee plant that would yield beans containing no caffeine, the synthesis of a substance known to be integral to the initial stages of caffeine production was blocked either in the beans, in the leaves, or both. For those plants in which synthesis of the substance was blocked only in the leaves, the resulting beans contained no caffeine. Any of the following, if true, would provide the basis for an explanation of the observed results EXCEPT:

Laminated glass is much harder to break than the glass typically used in the windows of cars driven in Relnia. It is more difficult for thieves to break into cars with laminated glass windows than into cars with ordinary glass windows, and laminated glass windows are less likely to break in a collision. Nevertheless, considerations of security and safety do not unambiguously support a proposal to require that in Relnia all glass installed in cars be laminated glass, since __________. Which of the following most logically completes the passage?

Consultant: **Ace Repairs ends up having to redo a significant number of the complex repair jobs it undertakes, but when those repairs are redone, they are invariably done right.** Since we have established that there is no systematic difference between the mechanics who are assigned to do the initial repairs and those who are assigned to redo unsatisfactory jobs, we must reject the hypothesis that mistakes made in the initial repairs are due to the mechanics’ lack of competence. Rather, it is likely that **complex repairs require a level of focused attention that the company’s mechanics apply consistently only to repair jobs that have not been done right on the first try.** In the consultant’s reasoning, the two portions in boldface play which of the following roles?

To reduce waste of raw materials, the government of Sperland is considering requiring household appliances to be broken down for salvage when discarded. To cover the cost of salvage, the government is planning to charge a fee, which would be imposed when the appliance is first sold. Imposing the fee at the time of salvage would reduce waste more effectively, however, because consumers tend to keep old appliances longer if they are faced with a fee for discarding them. Which of the following, if true, most seriously weakens the argument?

Twelve years ago and again five years ago, there were extended periods when the Changir Republic’s currency, the pundra, was weak: Its value was unusually low relative to the world’s most stable currencies. Both times, a weak pundra made Changir’s manufactured products a bargain on world markets, and Changir’s exports were up substantially. Now some politicians are saying in order to cause another similarly sized increase in exports, the government should allow the pundra to become weak again. Which of the following, if true, provides the government with the strongest grounds to doubt that if followed, the politicians’ recommendation will achieve its aim?

Increased use of incineration is sometimes advocated as a safe way to dispose of chemical waste. But opponents of incineration point to the 40 incidents involving unexpected releases of dangerous chemical agents that were reported just last year at two existing incinerators commissioned to destroy a quantity of chemical waste material. Since designs for proposed new incinerators include no additional means of preventing such releases, leaks will only become more prevalent if use of incineration increases. Which of the following, if true, most seriously weakens the argument?

Public health expert: **Increasing the urgency of a public health message may be counterproductive.** In addition to irritating the majority who already behave responsibly, **it may undermine all government pronouncements on health by convincing people that such messages are overly cautious.** And there is no reason to believe that those who ignore measured voices will listen to shouting. The two sections in boldface play which of the following roles in the public health expert’s argument?

A new machine for harvesting corn will allow rows to be planted only 15 inches apart instead of the usual 30 inches. Corn planted this closely will produce lower yields per plant. Nevertheless, the new machine will allow corn growers to double their profits per acre because __________. Which of the following most logically completes the argument?

The difference in average annual income in favor of employees who have college degrees, compared with those who do not have such degrees, doubled between 1980 and 1990. Some analysts have hypothesized that increased competition between employers for employees with college degrees drove up income for such employees. Which of the following, if true, most seriously undermines the explanation described above?

According to the last pre-election poll in Whippleton, most voters believe that the three problems government needs to address, in order of importance, are pollution, crime, and unemployment. Yet in the election, candidates from parties perceived as strongly against pollution were defeated, while those elected were all from parties with a history of opposing legislation designed to reduce pollution. These results should not be taken to indicate that the poll was inaccurate, however, since __________. Which of the following most logically completes the passage?

Manufacturing plants in Arundia have recently been acquired in substantial numbers by investors from abroad. Arundian politicians are proposing legislative action to stop such investment, justifying the proposal by arguing that foreign investors, opportunistically exploiting a recent fall in the value of the Arundian currency, were able to buy Arundian assets at less than their true value. Which of the following, if true, casts the most serious doubt on the adequacy of the Arundian politicians’ justification for the proposed legislation?

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?

Proposed new safety rules for Beach City airport would lengthen considerably the minimum time between takeoffs from the airport. In consequence, the airport would be able to accommodate 10 percent fewer flights than currently use the airport daily. The city’s operating budget depends heavily on taxes generated by tourist spending, and most of the tourists come by plane. Therefore, the proposed new safety rules, if adopted, will reduce the revenue available for the operating budget. The argument depends on assuming which of the following?

The introduction of new drugs into the market is frequently prevented by a shortage of human subjects for the clinical trials needed to show that the drugs are safe and effective. Since the lives and health of people in future generations may depend on treatments that are currently experimental, practicing physicians are morally in the wrong when, in the absence of any treatment proven to be effective, they fail to encourage suitable patients to volunteer for clinical trials. Which of the following, if true, casts most doubt on the conclusion of the argument?

As a construction material, bamboo is as strong as steel and sturdier than concrete. Moreover, in tropical areas, bamboo is a much less expensive construction material than either steel or concrete and is always readily available. In tropical areas, therefore, building with bamboo makes better economic sense than building with steel or concrete, except where land values are high. Which of the following, if true, most helps to explain the exception noted above?