17. Since 1975 there has been in the United States a dramatic decline in the incidence of traditional childhood diseases such as measles. This decline has been accompanied by an increased incidence of Peterson’s disease, a hitherto rare viral infection, among children. Few adults, however, have been affected by the disease.
Which of the following, if true, would best help to explain the increased incidence of Peterson’s disease among children?
(A) Hereditary factors determine in part the degree to which a person is susceptible to the virus that causes Peterson’s disease.
(B) The decrease in traditional childhood diseases and the accompanying increase in Peterson’s disease have not been found in any other country.
(C) Children who contract measles develop an immunity to the virus that causes Peterson’s disease.
(D) Persons who did not contract measles in childhood might contract measles in adulthood, in which case the consequences of the disease would generally be more severe.(C)
(E) Those who have contracted Peterson’s disease are at increased risk of contracting chicken pox.
18. Many plant varieties used in industrially developed nations to improve cultivated crops come from less developed nations. No compensation is paid on the grounds that the plants used are “the common heritage of humanity.” Such reasoning is, however, flawed. After all, no one suggests that coal, oil, and ores should be extracted without payment.
Which of the following best describes an aspect of the method used by the author in the argument above?
(A) The author proceeds from a number of specific observations to a tentative generalization.
(B) The author applies to the case under discussion facts about phenomena assumed to be similar in some relevant respect.
(C) A position is strengthened by showing that the opposite of that position would have logically absurd consequences.
(D) A line of reasoning is called into question on the grounds that it confuses cause and effect in a causal relation.(B)
(E) An argument is analyzed by separating statements of fact from individual value judgments.
19. It is widely assumed that a museum is helped financially when a generous patron donates a potential exhibit. In truth, however, donated objects require storage space, which is not free, and routine conservation, which is rather expensive. Therefore, such gifts exacerbate rather than lighten the demands made on a museum’s financial resources.
Which of the following, if true, most seriously weakens the argument above?
(A) To keep patrons well disposed, a museum will find it advisable to put at least some donated objects on exhibit rather than merely in storage.
(B) The people who are most likely to donate valuable objects to a museum are also the people who are most likely to make cash gifts to it.
(C) A museum cannot save money by resorting to cheap storage under less than adequate conditions, because so doing would drive up the cost of conservation.
(D) Patrons expect a museum to keep donated objects in its possession rather than to raise cash by selling them.(E)
(E) Objects donated by a patron to a museum are often of such importance that the museum would be obliged to add them to its collection through purchase if necessary.
20. Despite the approach of winter, oil prices to industrial customers are exceptionally low this year and likely to remain so. Therefore, unless the winter is especially severe, the price of natural gas to industrial customers is also likely to remain low.
Which of the following, if true, provides the most support for the conclusion above?
(A) Long-term weather forecasts predict a mild winter.
(B) The industrial users who consume most natural gas can quickly and cheaply switch to using oil instead.
(C) The largest sources of supply for both oil and natural gas are in subtropical regions unlikely to be affected by winter weather.
(D) The fuel requirements of industrial users of natural gas are not seriously affected by the weather.(B)
(E) Oil distribution is more likely to be affected by severe winter weather than is the distribution of natural gas.
编辑推荐：
