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托福培训
托福考试动态
2017-02-10 13:53
来源：网络
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A Wolf in Coyote’s Clothing
It’s nighttime. All is still. Suddenly, themournful howl of a coyote drifts through the crisp night air. This isn’t theNew Mexico desert or the 1 plains of Wyoming. This is downtown Chicago, NewYork City’s Central Park, or suburban Connecticut. Over the past severaldecades, coyotes have been moving steadily eastward and showing up in 2 unexpectedplaces. But that’s not all that’s strange about these eastern coyotes:They’re also bigger than their western cousins. They live in groups and hunt inpacks, 3 whereasWestern coyotes are solitary and hunt alone. The differences piquedscientists’ curiosity.
4 Now, recent genetic studies haveconfirmed what many experts had suspected. The eastern “coyotes” are actually“coy-wolves”—that is, coyote-wolf hybrids. Different eastern coyote populationshave different exact genetic 5 compositions, which scientists have describedthe average eastern coyote as being a combination of three different species inthe genus Canis. Specifically, the animals are mostly coyote, with a sizablewolf contribution, and a little bit of domestic dog thrown in for good measure.These three species can produce viable, fertile offspring because they all have39 pairs of chromosomes. 6 Most animals prefer to mate within their own species butsometimes, where there are small populations and few choices of mates,hybridization can occur. When it does, the offspring 7 resembles somethingin between their two parent species. The animals will have a new set of traits.In many cases, these traits 8 will often turn out to be neutral or evennegative.
In the case of the eastern coyote, however,it seems that the genetic contribution from wolves has actually been the key tothe animals’ success and expansion. 9 In the second half of the twentiethcentury, more of the population moved to cities and suburbs, and fewer acreshave been needed for agriculture. Consequently, much of the land has been slowlyreverting to forest.
With ample habitat and no 10 predators,species such as the white-tailed deer have populated the eastern U.S.in unprecedented numbers. Western coyotes—small and solitary hunters—are nomatch for even injured or young deer. 11 Hunting in packs by the largereastern coyotes, the oversaturated deer population can be seriously impacted. Evolutionis a process continuing all around us, and it doesn’t always take millions andmillions of years. As genetic tools get more sophisticated, sometimes we caneven catch it in action.
1
NO CHANGE
plains’ of Wyoming.
plain’s of Wyoming.
Wyoming plains’.
2
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out of the blue locations.
totally random hangouts.
wondrous positions.
3 The writer is considering deleting theunderlined portion and ending the sentence with a period. Should the writermake this revision?
No, because the informationprovides additional detail about visual differences between eastern and westerncoyotes.
No, because the informationcompletes the contrast between the behavior of the eastern and western coyotes.
Yes, because the informationprovides irrelevant detail about western coyotes while the author is discussingeastern coyotes.
Yes, because the informationrefutes what the author has already said about coyote traits.
4 Which choice most effectively establishes themain topic of the paragraph?
The eastern coyotes areactually coyote-wolf hybrids.
Wolves and coyotes interbreedin places where they share a habitat and population numbers are low.
Eastern coyotes are skillfulhunters that have managed to take down larger prey animals than wolves.
The genus Canis is composed ofdog-like animals from all over the world - wolves, dogs, dingoes, and jackals.
5
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compositions that
compositions then
compositions, but
6 At this point, the writer wants to illustratethe concept introduced in the preceding sentence by using another species as anexample. Which choice best accomplishes this goal?
Moreover, wolves and coyotesshare the same breeding season and habits.
In contrast, when horses anddonkeys interbreed, they produce mules, which are sterile due to their oddnumber of chromosomes.
However, higher numbers ofchromosomes do not correspond with more sophisticated organisms; humans onlyhave 23 pairs of chromosomes.
In theory, jackals caninterbreed with wolves and coyotes, but they do not live in North America.
7
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resembled
resemble
has resembled
8
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oftentimes will result astraits that are
will turn out to be
will turn out as resultingtraits that are
9 At this point, the writer wants to givehistorical context for changes in the environment. Which choice bestaccomplishes that goal?
Settlers had wiped out largepredators like wolves and mountain lions in the eastern portion of the UnitedStates by the beginning of the nineteenth century, leaving the ecosystemwithout an apex predator.
Wolves, with their larger sizeand adaptation to colder environments, are more effective predators in northernlatitudes than coyotes.
Some other hybrid animals, likethe offspring of tigers and lions, tend to take after one parent much more thanthe other, usually the mother.
The coyote population inwestern states has stayed steady over the twentieth century, while the wolfpopulation in the northern United States and Canada has dwindled.
10
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predators species, such as
predators, species, such as
predators species such as
11
NO CHANGE
Hunting in packs, the largereastern coyotes can have a serious impact on the oversaturated deer population.
Hunting in packs, a seriousimpact can be had on the oversaturated deer population by the larger easterncoyotes.
The oversaturated deerpopulation, by the larger eastern coyotes being hunted in packs, can beseriously impacted.
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托福培训
托福考试动态
