GMAT逻辑总纲-2

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二. 第二种文章（因果结构）：   A(事实)<---(因果)------B(推测原因)   
第三种文章（变态结构）：     A(事实)<----(前提结论:因果)-------B(推测)   
                                 
第二种文章的标志词： 文中：A is due to B; A is attribute to B; A is result of B;
                     blame B on/for A; B is responsible for A; credit A to B.
                     问题中：explanation, interpretation, hypothesis.
第三种文章的标志词： 与第一种文章相同，表面上是前提结论结构，实质为因果结构，     
                     即结论是前提的解释。

1.    削弱。
(1)    断桥型。 非B, A  ;  B, 非A  
例1. Artificial seaweed made of plastic has been placed on a section of coast in order to reverse beach
erosion. The inventor of the seaweed has concluded that the recent buildup of sand on that section of
coast proves that the artificial seaweed reverses beach erosion.
  Which of the following, if true, world most seriously weaken the inventor’s conclusion?
(A) The amount of recent sand buildup on that section of coast was less than had been predicted on
the basis of the results obtained in controlled experiments.
(B) Because artificial seaweed would be buried eventually by additional sand deposits on the coast,
more artificial seaweed would need to be put in place every four years.
(C) Artificial seaweed of another material which had been previously developed by the inventor
failed to add sand to coastline in past trials.
(D) The amount of recent sand buildup on that section of coast is the same as the amount of recent
sand buildup on otherwise very similar sections of coast without artificial seaweed.
(E) The amount of recent sand buildup on that section of coast, although considerable, is not yet
enough to replace the amount lost during storms on that section of coast in the last twenty years.

例2. The presence of microorganisms that produce a toxin cause seawater  to turn brownish red,
phenomenon known as a red tide. Sea otters do not feed in areas where clams, their main source of food, have become contaminated with this toxin. According to a proposed explanation of the otter’s behavior, the otters sample the clams in a potential feeding area and can taste any toxin in them.
  Which of the following, if true, would most strongly indicate that the hypothesis described in the last
sentence of the passage of the passage is not correct?
(A) In some of the area where red tides occur, neither clams nor sea otters are indigenous species.
(B) The presence of sea otters in a given area has a significant effect on which other marine
organisms are to be found in that areas.
(C) When seawater in an area unaffected by red tide is artificially dyed brownish red, sea otters do
not feed on the clams in that area.
(D) If the clams in a given areas are contaminated with toxin, sea otters move to other areas in search
of food.
(E) Although very small amounts of the toxin produced during a red tide are not harmful, large doses
can be fatal to animals the size of sea otters.

例3. Since 1945 there have been numerous international confrontations as tense as those that precipitated
the Second World War, and yet no large-scale conflict has resulted. To explain this, some argue that
fear of enormous destruction such as the Second War produced has had a dramatic deterrent effect.
  Which of the following, if true, most seriously weakens the deterrent theory mentioned above?
(A) After the First World War, the fear of great future destruction was as intense as it was after the
Second World War.
(B) Psychologists have determined that the fear of retaliation tends to temper aggressiveness among
human beings.
(C) The Second World War was far less distractive than most people generally believe.
(D) Fear of repeating the levels of destruction that the Second World War produced is as pervasive
today as it was forty years ago.
(E) Many of the international confrontations that have occurred since 1945 have involved countries
that participated in the Second World War.

(2)    他因, C -->A
例. The price of maple syrup has jumped from 22 dollars a gallon three years ago to 40 dollars a gallon
today. It can be concluded that maple-syrup harvesters have been artificially inflating prices and that
governmental price regulations are necessary to control rising prices.
  Which of the following, if true, casts the most doubt on the conclusion drawn above?
(A) The government already requires maple-syrup harvesters to submit their facilities to licensing by
the health department.
(B) Insect infestation and drought have stunted the growth of syrup-producing maple trees and
caused less-abundant syrup harvests.
(C) Maple syrup is produced in rural areas that suffer from high unemployment.
(D) Technological improvements in maple-syrup harvesting have reduced production costs.
(E) Maple-syrup prices have risen many times in the past, though never before at the rate recently
observed.
2.    加强。
桥梁型, 非B, 非 A
例1. The population of peregrine falcons declined rapidly during the 1950’s and 1960’s and reached an
all-time low in the early 1970’s. The decline was attributed by scientists to the widespread use of the
pesticide DDT in rural areas.
  Which of the following, if true, gives the strongest support to the scientists claim?
(A) DDT was not generally in use in areas devoted to heavy industry.
(B) In the time since the use of DDT was banned in 1972, the population of peregrine falcons has
been steadily increasing.
(C) Peregrine falcons, like other birds of prey, abandon eggs that fallen out of the nest, even if the
eggs remain intact.
(D) Starling, house sparrows, and blue jays-birds the peregrine falcon prey on—were not adversely
affected by DDT in their habitats.
(E) Other birds of prey, such as the osprey, the bald cage, and the brown pclican, are found in the
same area as is the peregrine falcon.

例2. The town of Stavanger, Norway, was quiet and peaceful until early 1960’s, when Stavanger became
Norway’s center for offshore oil exploration. Between then and now, violent crime and vandalism in
Stavanger have greatly increased. Clearly, these social problems are among the results of Stavanger’s
oil boom.
  Which of the following, if it occurred between the early 1960’s and now, gives the strongest support
to the argument above?
(A) The people of Stavanger rarely regret that their town was chosen to be Norway’s center for
offshore oil exploration.
(B) Norwegian sociologists expressed grave concern about the increase in violent crime and
vandalism in Stavanger.
(C) Violent crime and vandalism have remained low in Norwegian that had no oil boom.
(D) Nonviolent crime, drug addiction, and divorce in Stavanger increased approximately as much as
violent crime and vandalism did.
(E) The oil boom necessitated the building of wider roads for the increased traffic in Stavanger.

3.    评价。
当加强来做。
三. 假设题补充。
   not + weaken
例1. In the 1960’s long-term studies of primate behavior often used as subjects tamaris, small monkeys
that were thought ideal because they require only small cages, breed frequently, and grow quickly.
Field studies were not used because they were costly and difficult. Tamarinds were kept caged in
male-female pairs, because otherwise, serious fights erupted between unrelated females. On the basis
of the fact that breeding occurred, tamarinds were viewed as monogamous.
  The view taken by the researchers concerning the monogamy of tamarinds deepened on a questionable
assumption. Which of the following could have served as that assumption?
(A) The suppression of fighting between related females serves to protect their common genetic
inheritance.
(B) Adult male tamarinds contribute to the care of tamarind infants.
(C) The social system of tamarinds requires monogamous pairing.
(D) Male tamarind monkeys do not display aggressive behavior in the wild.
(E) The way the tamarinds were kept in cages did not affect their mating behavior.

例2. Twenty percent of all energy consumed in the United States is consumed by home appliances. If
appliances that are twice as energy-efficient as those currently available are produced, this figure will
eventually be reduced to about ten percent.
  The argument above requires which of the following assumption?
(A) Home-appliance usage would not increase along with the energy efficiency of the appliances.
(B) It would not be expensive to produce home appliances that are energy-efficient.
(C) Home-appliance manufacturers now have the technology to produce appliances that are twice as
energy-efficient as those currently available.
(D) The cost of energy to the consumer world rise with increase in the energy efficiency of home
appliances.
(E) The percentage of energy consumed by home appliances will increase if existing appliances are
not replaced by more energy-efficient models.

例3. Inspection system X and inspection system Y, though based on different principles, each detect all
product flaws but they each also erroneously reject three percent of flawless products. Since false
rejections are very costly, monkey will be saved by installing both systems, instead of either one or
the other, and rejecting only products found flawed by both.
The argument above requires which of the following assumption?
(A)    The three percent of flawless products that system X rejects are not all the same products, piece for piece, that system Y erroneously rejects.
(B)    It is less costly to accept a flawed product than to reject a flawless one.
(C)    In their price range, system as X and Y are the least error-prone inspection systems on the market.
(D)    Whichever system performs the second inspection needs to inspect only products not rejected by the first system.
(E)    Any way of detecting flaws, other than by using either system X or system Y, requires complete disassembly of the products.

例4. 染上t这种病的人一次又一次重复发作。这就证明了t这种病从未被根治过。
假设？（关于这种人）
(A) 不可能被完全根治t。
(B) 并不理解什么导致t。
(C) 未获得t的药物治疗。
(D) 不采取步骤避免得t。
(E) 并未重复感染上t。

例5. Statistics over four consecutive years showed that four percent more automobile accidents happened
in California during the week following the switch to daylight saving time and during the week
following the switch back to standard time than occurred the week before each event. These statistics
show that these time changes adversely affect the alertness of California drivers.
  The conclusion in the argument above is based on which of the following assumptions?
(A)    Drivers in California as well as those in the rest of the United States have similar driving patterns.
(B)    The observed increases in accident rates are due almost entirely to an increase in the number of minor accidents.
(C)    Four years is not a sufficiently long period of time over which to judge the phenomenon described.
(D)    There are no other factors such as school vacations or holiday celebrations that cause accident rates to rise during these weeks.
(E)    A time change at any other time of year would not produce a similar increase in accident

例6．Although the ratio of physicians to total population is about the same in the United State and Canada, the United States has 33 percent more surgeons per capita. Clearly, this is the reason people in the United States undergo 40 percent more operations per capita than do Canadians.
The explanation given above rests on an assumption that
(A)patients in the United States do not have a greater need for surgery than do patients in Canada.
(B)the population of the United States is not larger than that of Canada.
(C)United States patients sometimes travel to Canada for certain kinds of surgery.
(D)general practitioners in the United States do not as a rule examine a patient who is a candidate for surgery before sending the patient to a surgeon.
(E)there are no unnecessary surgical operations performed in Canada.

[此贴子已经被作者于2003-8-30 13:16:46编辑过]