16.A researcher studying drug addicts found that， on average， they tend to manipulate other people a great deal more than nonaddicts do. The researcher concluded that people who frequently manipulate other people are likely to become addicts.

Which of the following， if true， most seriously weakens the researcher's conclusion？

（A） After becoming addicted to drugs， drug addicts learn to manipulate other people as a way of obtaining drugs.

（B） When they are imprisoned， drug addicts often use their ability to manipulate other people to obtain better living conditions.

（C） Some nonaddicts manipulate other people more than some addicts do.

（D） People who are likely to become addicts exhibit unusual behavior patterrns other than frequent manipulation of other people.

17.Advertisement：For sinus pain， three out of four hospitals give their patients Novex So when you want the most effective painkiller for sinus pain， Novex is the one to choose.

Which of the following， if true， most seriously ndermines the advertisement's argument？

（A） Some competing brands of painkillers are intended to reduce other kinds of pain in addition to sinus pain.

（B） Many hospitals that do not usually use Novex will do so for those patients who cannot tolerate the drug the hospitals usually use.

（C） Many drug manufacturers increase sales of their products to hospitals by selling these products to the hospitals at the lowest price the manufacturers can afford.

（D） Unlike some competing brands of painkillers， Novex is available from pharmacies without a doctor's prescription.

（E） In clinical trials Noxvex has been found more effective than competing brands of painkillers that have been on the market longer than Novex.

18.Hardin argued that grazing land held in common （that is， open to any user） would always be used less carefully than private grazing land. Each rancher would be tempted to overuse common land because the benefits would accrue to the individual， while the costs of reduced land quality that results from overuse would be spread among all users. But a study comparing 217 million acres of common grazing land with 433 million acres of private grazing land showed that the common land was in better condition.

The answer to which of the following questions would be most useful in evaluating the significance， in relation to Hardin's claim， of the study described above？

（A） Did any of the ranchers whose land was studied use both common and private land？

（B） Did the ranchers whose land was studied tend to prefer using common land over using private land for grazing？

（C） Was the private land that was studied of comparable quality to the common land before either was used for grazing？

（D） Were the users of the common land that was studied at least as prosperous as the users of the private land？

（E） Were there any owners of herds who used only common land， and no private land， for grazing？

19.Guitar strings often go “dead”-become less responsive and bright in tone-after a few weeks of intense use. A researcher whose son is a classical guitarist hypothesized that dirt and oil， rather than changes in the material properties of the string， were responsible.

Which of the following investigations is most likely to yield significant information that would help to evaluate the researcher's hypothesis？

（A） Determining if a metal alloy is used to make the strings used by classical guitarists

（B） Determining whether classical guitarists make their strings go dead faster than do folk guitarists

（C） Determining whether identical lengths of string， of the same gauge， go dead at different rates when strung on various brands of guitars.

（D） Determining whether a dead string and a new string produce different qualities of sound

（E） Determining whether smearing various substances on new guitar string cause them to go dead

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