Sunflowers growing in pots were placed, with their roots submerged, in the pond contaminated with radioactive elements. The sunflowers kept growing; in the process, they absorbed radioactive elements. Within twelve days, 85 percent of the radioactive elements were removed from the water, which is no less than can be accomplished with the much more expensive conventional filtration techniques. Scientists therefore propose using sunflowers for decontamination wherever there are radioactively contaminated ponds.

Which of the following, if true, points to a limitation on the applicability of the proposed method of decontamination?

In the past, most children who went sledding in the winter snow in Verland used wooden sleds with runners and steering bars. Ten years ago, smooth plastic sleds became popular; they go faster than wooden sleds but are harder to steer and slow. The concern that plastic sleds are more dangerous is clearly borne out by the fact that the number of children injured while sledding was much higher last winter than it was ten years ago.

Which of the following, if true in Verland, most seriously undermines the force of the evidence cited?

SafeZone mosquito repellant has been shown in laboratory settings to be effective for twelve hours against the female anopheles mosquito, the only mosquito that transmits malaria. SafeZone, however, is not effective against mosquitoes that do not transmit malaria. The only instance in which SafeZone does not repel the female anopheles mosquito is when this mosquito can detect any ruptured blood vessels, a state that inevitably results whenever any kind of mosquito bites a person. Therefore, assuming one does not have any ruptured blood vessels on their skin before applying SafeZone, that person will not be able to catch malaria for up to twelve hours.Which of the following, if true, would argue most against the use of SafeZone in areas in which malaria is endemic?

Nearly all employees of the factory who have completed their high school diploma have earned their factory safety certificate, having easily completed the eight week training course. The high school graduates who haven't earned the certificate are ones who have evening obligations that have prevented them from taking the course. Overall, though, most of the factory workers have not earned the certificate. If the statements above are true, which one of the following also must be true?

During the period in which there are no competitive races, two runners--Runners A and Runners B--take part in an experiment measuring their VO2 max, the volume of oxygen an athlete can use. During these sessions, the runners engaged in moderate aerobic activity, or a sustained heart rate between 146-154 beats per minute. At the end of the sessions, Runner A had a greater VO2 max than did Runner B. Therefore, once the two runners begin identical intensive training--sessions involving over 168 beats per minute-- for the race season, Runner A will continue to have the greater VO2 max, assuming that neither become injured and that both train with similar intensity.Which of the following is an assumption upon which the argument rests?

In Patton City, days are categorized as having heavy rainfall (more than two inches), moderate rainfall (more than one inch, but no more than two inches), light rainfall (at least a trace, but no more than one inch), or no rainfall. In 1990, there were fewer days with light rainfall than in 1910 and fewer with moderate rainfall, yet total rainfall for the year was 20 percent higher in 1990 than in 1910.

If the statements above are true, then it is also possible that in Patton City

During the past year, Pro-Tect Insurance Company's total payouts on car-theft claims were larger than the company can afford to sustain. Pro-Tect cannot reduce the number of car-theft policies it carries, so cannot protect itself against continued large payouts that way. Therefore, Pro-Tect has decided to offer a discount to holders of car-theft policies whose cars have antitheft devices. Many policyholders will respond to the discount by installing antitheft devices, since the amount of the discount will within two years typically more than cover the cost of installation. Thus, because cars with antitheft devices are rarely stolen, Pro-Tect's plan is likely to reduce its annual payouts.

In the argument above, the two portions in boldface play which of the following roles?

In Kantovia, physicians' income comes from insurance companies, which require physicians to document their decisions in treating patients and to justify deviations from the companies' treatment guidelines. Ten years ago physicians were allowed more discretion. Most physicians believe that the companies' requirements now prevent them from spending enough time with patients. Yet the average amount of time a patient spends with a physician during an office visit has actually increased somewhat over the last ten years.

Which of the following, if true, most helps to resolve the apparent discrepancy between physicians' perceptions and the change in the actual time spent?

Consumers planning to buy recreational equipment tend to buy higher quality, more expensive equipment when the economy is strong than when it is weak. Hill and Dale is a business that sells high-quality, expensive camping and hiking equipment in Boravia. Although all the signs are that Boravia's economy is now entering a period of sustained strength, the managers of the business do not expect a substantial increase in sales.

Which of the following, if true, would provide the strongest justification for the managers' judgment?

Which of the following, if true, provides evidence that most logically completes the argument below?

According to a widely held economic hypothesis, imposing strict environmental regulations reduces economic growth. This hypothesis is undermined by the fact that the states with the strictest environmental regulations also have the highest economic growth. This fact does not show that environmental regulations promote growth, however, since ______.

Whales originated in the freshwater lakes and rivers of ancient Asia about sixty million years ago. Not until about ten million years later did species of whales develop specialized kidneys enabling them to drink salt water. Although fossil evidence shows that some early whale species that lacked such kidneys sometimes swam in the Earth's saltwater oceans, these species must have had to return frequently to freshwater rivers to drink.

Which of the following is most strongly supported by the information given?

Manatees, aquatic mammals inhabiting Florida's rivers and coastal waters, swim close to the surface and are frequently killed in collisions with boats. To address the problem, boat traffic in manatee-populated waters is being required to maintain very low speeds. Unfortunately, manatees are unable to hear low-pitched sounds and a boat's sound lowers in pitch as the boat slows. Therefore, this approach may in fact make things worse rather than better.

Which of the following, if true, casts most doubt on the conclusion?

The total market value of real estate in Altonville has steadily declined over the past four years. This decline has meant that the overall figure on which the city's property tax is based-the assessed value of that real estate-has also declined. The percentage of assessed value that was paid as property taxes to the city, however, did not change from year to year during this period.

The information above most strongly supports which of the following?

Though sucking zinc lozenges has been promoted as a treatment for the common cold, research has revealed no consistent effect. Recently, however, a zinc gel applied nasally has been shown to greatly reduce the duration of colds. Since the gel contains zinc in the same form and concentration as the lozenges, the greater effectiveness of the gel must be due to the fact that cold viruses tend to concentrate in the nose, not the mouth.

In order to evaluate the argument, it would be most helpful to determine which of the following?

Astronomer: Observations of the Shoemaker-Levi comet on its collision course with Jupiter showed that the comet broke into fragments before entering Jupiter's atmosphere in 1994, but they did not show how big those fragments were. Nevertheless, some indication of their size can be inferred from spectrographic analyses of Jupiter's outer atmosphere. After the fragments' entry, these analyses revealed unprecedented traces of sulfur. The fragments themselves almost certainly contained no sulfur, but astronomers believe that the cloud layer below Jupiter's outer atmosphere does contain sulfur. Since sulfur would have seeped into the outer atmosphere if comet fragments had penetrated this cloud layer, it is likely that some of the fragments were at least large enough to have passed through Jupiter's outer atmosphere without being burned up.

In the astronomer's argument, the two portions in boldface play which of the following roles?