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　　14.The sustained massive use of pesticides in farming has two effects that are especially pernicious.First, it often kills off the pests’ natural enemies in the area.Second，it often unintentionally gives rise to insecticide-resistant pests，since those insects that survive a particular insecticide will be the ones most resistant to it，and they are the ones left to breed.

　　From the passage above，it can be properly inferred that the effectiveness of the sustained massive use of pesticides can be extended by doing which of the following，assuming that each is a realistic possibility?

　　(A) Using only chemically stable insecticides

　　(B) Periodically switching the type of insecticide used

　　(C) Gradually increasing the quantities of pesticides used

　　(D) Leaving a few fields fallow every year

　　(E) Breeding higher-yielding varieties of crop plants

　　15. Treatment for hypertension forestalls certain medical expenses by preventing strokes and heart disease.Yet any money so saved amounts to only one—fourth of the expenditures required to treat the hypertensive population.Therefore，there is no economic 1ustification for preventive treatment for hypertension.

　　Which of the following，if true，is most damaging to the conclusion above?

　　(A) The many fatal strokes and heart attacks resulting from untreated hypertension cause insignificant medical expenditures but large economic losses of other sorts.

　　(B) The cost，per patient，of preventive treatment for hypertension would remain constant even if such treatment were instituted on a large scale.

　　(C) In matters of health care.Economic considerations should ideally not be dominant.

　　(D) Effective prevention presupposes early diagnosis，and programs to ensure early diagnosis are costly.

　　(E) The net savings in medical resources achieved by some preventive health measures are smaller than the net losses attributable to certain other measures of this kind.

　　16. In an attempt to promote the widespread use of paper rather than plastic，and thus reduce non-biodegradable waste，the council of a small town plans to ban the sale of disposable plastic goods for which substitutes made of paper exist.The council argues that since most paper is entirely biodegradable，paper goods are environmentally preferable.

　　Which of the following，if true，indicates that the plan to ban the sale of disposable plastic goods is suited to the town council’s environmental goals?

　　(A) Although biodegradable plastic goods are now available，members of the town council believe biodegradable paper goods to be safer for the environment.

　　(B) The paper factory at which most of the townspeople are employed plans to increase production of biodegradable paper goods.

　　(C) After other towns enacted similar bans on the sale of plastic goods，the environmental benefits were not discernible for several years.

　　(D) Since most townspeople prefer plastic goods to paper goods in many instances，they are likely to purchase them in neighboring towns where plastic goods are available for sale.

　　(E) Products other than those derived from wood pulp are often used in the manufacture of paper goods that are entirely biodegradable.

　　17. Since the deregulation of airlines，delays at the nation’s increasingly busy airports have increased by 25 percent.To combat this problem，more of the takeoff and landing slots at the busiest airports must be allocated to commercial airlines.

　　Which of the following，if true，casts the most doubt on the effectiveness of the solution proposed above?

　　(A) The major causes of delays at the nation’s busiest airports are bad weather and overtaxed air traffic control equipment.

　　(B) Since airline deregulation began，the number of airplanes in operation has increased by 25 percent.

　　(C) Over 60 percent of the takeoff and landing slots at the nation’s busiest airports are reserved for commercial airlines.

　　(D) After a small Midwestern airport doubled its allocation of takeoff and landing slots，the number of delays that were reported decreased by 50 percent.

　　(E) Since deregulation the average length of delay at the nation’s busiest airports has doubled.

　　18. Unlike the wholesale price of raw wool，the wholesale price of raw cotton has fallen considerably in the last yean Thus，although the retail price of cotton clothing at retail clothing stores has not yet fallen，it will inevitably fall.

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

　　(A) The cost of processing raw cotton for cloth has increased during the last year.

　　(B) The wholesale price of raw wool is typically higher than that of the same volume of raw cotton.

　　(C) The operating costs of the average retail clothing store have remained constant during the last year.

　　(D) Changes in retail prices always lag behind changes in wholesale prices.

　　(E) The cost of harvesting raw cotton has increased in the last year

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