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2014年5月11日托福阅读真题+题目+答案：Costs and Benefits of Dispersal
In order to move from one home base to another, animals must expend calories not only while moving but even before the dispersal when they invest in the development of the muscles needed to move. For example, if a cricket is to leave a deteriorating environment and move to a new and better place, it will need large flight muscles to fly away. Presumably, the calories and materials that go into flight muscle development and maintenance have to come out of the general energy budget of the animal. This means that other organ systems cannot develop as rapidly as they could otherwise, which may mean that the flight-capable individual is, in some other respects, less fit to survive.
Dispersing individuals not only have to pay energetic, developmental, and travel costs but are also more often exposed to predators—all of which raises the question, why are animals so often willing to leave home even when this means leaving a familiar, resource-rich location? This question is particularly pertinent for species in which some individuals disperse while others do not or do not disperse as far. One species in which some individuals travel farther than others is Belding’s ground squirrel. Young male squirrels travel about 150 meters from the burrow in which they were born, whereas young females usually settle down only 50 meters or so from where they were born. Why should young Belding’s ground squirrels disperse at all, and why should the males disperse farther than their sisters?
According to one argument, dispersal by juvenile animals of many species may be an adaptation against problems associated with inbreeding. When two closely related individuals mate, their offspring are more likely to manifest genetic diseases than are the offspring of genetically unrelated individuals, and as a result, inbreeding tends to produce animals that are less likely to survive to adulthood and reproduce. Dispersal of juveniles makes inbreeding less likely.
If avoidance of inbreeding is the point of dispersing, then one might expect as many female ground squirrels as males to travel 150 meters from their natal burrow. In fact females do not disperse as far as males, perhaps because the costs and benefits of dispersal differ for the two sexes. It has been suggested that the reproductive success of female Belding’s ground squirrels depends on their possession of a territory in which to rear their young. Female ground squirrels that remain near their birthplace enjoy assistance from their mothers in the defense of their burrows against rival females. Thus, the benefits of remaining on familiar ground are greater for females than for males.
There may, however, be another reason why male mammals disperse greater distances than females. The usual rule is that males, not females, fight with one another for access to mates, and, therefore, males that lose such conflicts may find it advantageous to move away from same-sex rivals that they cannot subdue. Although this hypothesis probably does not apply to Belding’s ground squirrels, since young males have not been seen fighting with older ones around the time of dispersal, the idea is more plausible with respect to some other species, such as lions.
Lions live in large groups, or prides, from which young males disperse. In contrast, the daughters of the resident lionesses usually spend their entire lives close to where they were born. The sedentary females benefit from their familiarity with good hunting grounds and safe breeding dens in their natal territory, among other things. The departure of many young male lions coincides with the arrival of new mature males that violently displace the previous masters of the pride and chase off the males that are not yet adults in the pride as well. These observations support the mate-competition hypothesis for male dispersal. However, if young males are not evicted after a pride takeover, they often leave anyway without any coercion from adult males and without ever having attempted to mate with their female relatives. Moreover, mature males that have claimed a pride sometimes disperse again, expanding their range to add a second pride of females, at a time when their daughters in the first pride are becoming sexually mature. Inhibitions against inbreeding apparently exist in lions and cause males to leave home.
1. The word ”Presumably” in the passage is closet in meaning to
A. It is reasonable to assume
B. It is possible
C. It can be argued
D. It is certainly true
2. In paragraph 1, the discussion of cricket dispersal is used to illustrate which of the following principles?
A.For dispersing animals, the benefits of dispersal exceed the costs.
B. Dispersal always involves costs for the dispersing animal.
C. Only animals with the greatest fitness for survival are able to disperse.
D. Dispersal, as much as organ development, requires energy. Paragraph 1 is marked with an arrow [→]
3. The word ” pertinent” in the passage is closet in meaning to
4. According to paragraph 2, what is of particular interest about the dispersal of Belding’s ground squirrels?
A.Young squirrels disperse farther than adults.
B. Young squirrels disperse even from resource-rich areas.
C. The males and females have different patterns of dispersal.
D. They leave the mother’s burrow at an earlier age than other squirrels. Paragraph 2 is marked with an arrow [→]
5. It can be inferred from paragraph 2 that the phenomenon of dispersal
A.is difficult to observe in the wild
B.occurs for reasons that are not always immediately apparent
C.Is motivated by the desire to obtain more or better resources
D. has few benefits for most species Paragraph 2 is marked with an arrow [→]
6. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A.When closely related individuals mate, their offspring are likely to manifest genetic diseases that will probably be passed on to the next generation.
B. Genetic diseases inherited from parents that are not related make it less likely that the affected offspring will survive to adulthood and reproduce.
C. When two related individuals mate, their offspring may survive to adulthood, but they are unlikely to reproduce.
D. There is a tendency for the offspring of closely related parents to have genetic diseases that make it less likely they will survive and reproduce.
7. According to paragraph 4, young female Belding’s ground squirrels may remain closer to where they were born than do males in order to
A.avoid inbreeding with their male siblings
B. avoid competition with other females for territory
C. save energy they need to defend their burrows
D. benefit from their mothers’ help Paragraph 4 is marked with an arrow [→]
8. According to paragraph 5, the hypothesis that males disperse as a result of conflicts with other males is not supported in the case of Belding’s ground squirrels because
A.young male squirrels that lose fights to other males do not disperse
B. unlike most species, it is the females, not the males, that fight with each other
C. there is no evidence that young male squirrels fight with other males before dispersing
D. fights between males generally take place after the males have dispersed Paragraph 5 is marked with an arrow [→]
9. The word ”subdue” in the passage is closet in meaning to
10. According to paragraphs 5 and 6, the patterns of dispersal in Belding’s ground squirrels and lions are similar in which of the following ways?
A.Young males are forced to disperse by older males.
B. Avoiding inbreeding is probably not a factor in the explanation of the pattern of dispersal.
C. Males disperse when new siblings are born.
D. The males disperse farther than the females. Paragraphs 5 and 6 are marked with arrows [→]
11. The phrase ”coincides with” in the passage is closet in meaning to
A.is driven by
B. occurs at the same time as
C. makes possible
D. is a sign of
12. Why does the author provide the information that “if young males are not evicted after a pride takeover, they often leave anyway without any coercion from adult males and without ever having attempted to mate with their female relatives”?
A.To support the conclusion that made lions disperse to find mates to which they are not closely related
B. To indicate that the mate-competition hypothesis does not fully account for the dispersal of young male lions
C. To imply that young male lions voluntarily leave a pride that has been taken over because the adult males prevent them from mating within the pride
D. To indicate that males, not females, leave a pride after it has been taken over by adult males
Paragraph 4 ■If avoidance of inbreeding is the point of dispersing, then one might expect as many female
ground squirrels as males to travel 150 meters from their natal burrow. ■In fact females do not disperse as far as males, perhaps because the costs and benefits of dispersal differ for the two sexes. ■It has been suggested that the reproductive success of female Belding’s ground squirrels depends on their possession of a territory in which to rear their young. ■Female ground squirrels that remain near their birthplace enjoy assistance from their mothers in the defense of their burrows against rival females. Thus, the benefits of remaining on familiar ground are greater for females than for males.
13. Look at the four squares [■] that indicate where the following sentence could be added to the passage. However, inbreeding can be avoided without both males and their female relatives dispersing the same distance.
Where would the sentence best fit? Click on a square [■] to add the sentence to the passage.
14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points. Drag your choices to the spaces where they belong. To review the passage, click on View Text.
Many young animals disperse from where they are born. ● ● ●
1.There are a number of competing explanations of why animals disperse, but none of them is consistent with all the observed patterns of dispersal.
2.The reason there is little inbreeding among lions is that young males are driven away from their female relatives by the adult males who forcibly take over a lion pride.
3.Inbreeding significantly lowers the likelihood that offspring will survive, and so avoiding inbreeding is a significant benefit of dispersal.
4. Since males of most species must establish a territory for mating, dispersing of the males makes it more likely that most males will be able to reproduce.
5.There need to be significant benefits for a species to disperse because the requirements of dispersal involve energy costs and dangers for the dispersing individuals.
6. In mammal species, young males often leave their family group while related females benefit from remaining in close association with each other and their birthplace.
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