The population of desert tortoises in Targland's Red Desert has declined, partly because they are captured for sale as pets and partly because people riding all-terrain vehicles have damaged their habitat. Targland plans to halt this population decline by blocking the current access routes into the desert and announcing new regulations to allow access only on foot. Targland's officials predict that these measures will be adequate, since it is difficult to collect the tortoises without a vehicle.

Which of the following would it be most important to establish in order to evaluate the officials' prediction?

Charcoal from a hearth site in Colorado, 2,000 miles south of Alaska, is known to be 11,200 years old. Researchers reasoned that, 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?

Unprecedented industrial growth in the country of Remo has created serious environmental problems because factories there lack adequate pollution-control systems. Remo is developing a clean growth plan that includes environmental regulations that will require the installation of such systems. Since no companies in Remo currently produce pollution-control systems, the plan, if implemented, will create significant opportunities for foreign exporters to market pollution-control systems.

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

People with a certain eye disorder are virtually unable to see in moderately bright light, which seems to them unbearably intense, since the cells of their retinas are overwhelmed by moderately bright light. These people do, however, show normal sensitivity to most components of dim light. Their retinal cells are also not excessively sensitive to red components of moderately bright light.

The information above best supports which of the following hypotheses about people with the disorder described, if they have no other serious visual problems?

Because mining and refining nickel is costly, researchers have developed an alternative method for extracting nickel using Streptanthus polygaloides, a plant that absorbs and stores nickel from the soil as it grows. The researchers incinerated a crop of Streptanthus they grew in nickel-rich soil. By chemically extracting nickel from the ash, they produced 100 pounds of nickel per acre of land at a total cost per pound slightly above that of current mining.

Which of the following, if true, most strongly supports the conclusion that the use of Streptanthus to extract nickel will be commercially adopted?

A theory is either true or false. Galileo's observations of Jupiter's satellites showed that the Ptolemaic theory of the motion of celestial bodies is false. Therefore, since the Copernican theory of planetary motion is inconsistent with the Ptolemaic account, Galileo's observations of Jupiter's satellites proved the truth of the Copernican theory.

The argument above is open to the objection that it makes the questionable assumption that

The traditional treatment of strep infections has been a seven-day course of antibiotics, either penicillin or erythromycin. However, since many patients stop taking those drugs within three days, reinfection is common in cases where those drugs are prescribed. A new antibiotic requires only a three-day course of treatment. Therefore, reinfection will probably be less common in cases where the new antibiotic is prescribed than in cases where either penicillin or erythromycin is prescribed.

Which of the following, if true, most strengthens the argument?

Although most smoking-related illnesses are caused by inhaling the tar in tobacco smoke, it is addiction to nicotine that prevents most smokers from quitting. In an effort to decrease the incidence of smoking-related illnesses, lawmakers in Sandonia plan to reduce the average quantity of nicotine per cigarette by half over the next five years. Unfortunately, smokers who are already addicted to nicotine tend to react to such reductions by smoking correspondingly more cigarettes.

The information above most strongly supports which of the following predictions about the effects of implementing the Sandonian government's plan?

Which of following most logically completes the argument?

The last members of a now-extinct species of a European wild deer called the giant dear lived in Ireland about 16,000 years ago. Prehistoric cave paintings in France depict this animal as having a large hump on its back. Fossils of this animal, however, do not show any hump. Nevertheless, there is no reason to conclude that the cave paintings are therefore inaccurate in this regard, since ______.

Economist: Tropicorp, which constantly seeks profitable investment opportunities, has been buying and clearing sections of tropical forest for cattle ranching, although pastures newly created there become useless for grazing after just a few years. The company has not gone into rubber tapping, even though greater profits can be made from rubber tapping, which leaves the forest intact. Thus, some environmentalists conclude that Tropicorp has not acted wholly out of economic self-interest. However, these environmentalists are probably wrong. The initial investment required for a successful rubber-tapping operation is larger than that needed for a cattle ranch. Furthermore, there is a shortage of workers employable in rubber-tapping operations, and finally, taxes are higher on profits from rubber tapping than on profits from cattle ranching.

In the economist's argument, the two boldfaced portions play which of the following roles?