16.(Z19)Rabbits were introduced to Numa Island in the nineteenth century. Overgrazing by the enormous population of rabbits now menaces the island’s agriculture. The government proposes to reduce the population by using a virus that has caused devastating epidemics in rabbit populations elsewhere. There is, however, a chance that the virus will infect the bilby, an endangered native marsupial. The government’s plan, therefore, may serve the interests of agriculture but will clearly increase the threat to native wildlife.
Which of the following, if true, most seriously weakens the argument?
A. There is less chance that the virus will infect domestic animals on Numa than that it will infect bilbies.
B. There are no species of animals on the island that prey on the rabbits.
C. Overgrazing by rabbits endangers many of the plants on which bilbies feed.
D. The virus that the government proposes to use has been successfully used elsewhere to control populations of rabbits.
E. There is no alternative means of reducing the rabbit population that would involve no threat to the bilby.
17.(Z19)Mice that have been given morphine are very likely to develop blood poisoning because bacteria that normally reside in the intestine typically respond to morphine by migrating into the bloodstream. However, when mice are given both morphine and the new drug naltrexone, blood poisoning is much less frequent, although it does still occur. These results provide support for researchers’ prediction that naltrexone will turn out to be toxic to certain types of bacteria.
Which of the following, if discovered to be true, would most seriously weaken the support for the researchers’ prediction?
A. After being administered to mice, naltrexone does not pass from the bloodstream into the intestine.
B. Naltrexone inhibits morphine from triggering the migration of intestinal bacteria into the bloodstream.
C. Mice that have been given naltrexone but not morphine have no greater risk of developing blood poisoning than do mice that have not been given either substance.
D. The increased risk of blood poisoning is not the only harmful effect on mice of being given morphine.
E. Conditions other than the presence of intestinal bacteria in the bloodstream can cause blood poisoning in mice.
18.(Z20)Industrial accidents are more common when some of the people in safety-sensitive jobs have drinking problems than when none do. Since, even after treatment, people who have had drinking problems are somewhat more likely than other people to have drinking problems in the future, any employer trying to reduce the risk of accidents should bar anyone who has ever been treated for a drinking problem from holding a safety-sensitive job.
Which of the following, if true, most seriously undermines the argument above?
A. Some companies place employees who are being treated for drinking problems in residential programs and allow them several weeks of paid sick leave.
B. Many accidents in the workplace are the result of errors by employees who do not hold safety-sensitive jobs.
C. Workers who would permanently lose their jobs if they sought treatment for a drinking problem try instead to conceal their problem and continue working for as long as possible.
D. People who hold safety-sensitive jobs are subject to stresses that can exacerbate any personal problems they may have, including drinking problems.
E. Some industrial accidents are caused by equipment failure rather than by employee error.精彩内容第二页继续......
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