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题目：

Scientists have dated sharp-edged flakes of stone found in the fine-grained sediments of a dry riverbed in the Afar region of Ethiopia to between 2.52 and 2.60 million years ago, pushing back by more than 150,000 years the earliest date when it is known that humans made stone tools

选项:

A、when it is known that humans made
B、at which it is known that humans had made
C、at which humans are known to have made
D、that humans are known to be making
E、of humans who were known to make

答案:

C
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题目：

Parland's alligator population has been declining in recent years, primarily because of hunting. Alligators prey heavily on a species of freshwater fish that is highly valued as food by Parlanders, who had hoped that the decline in the alligator population would lead to an increase in the numbers of these fish available for human consumption. Yet the population of this fish species has also declined, even though the annual number caught for human consumption has not increased.

Which of the following, if true, most helps to explain the decline in the population of the fish species?

选项:

A、The decline in the alligator population has meant that fishers can work in some parts of lakes and rivers that were formerly too dangerous.
B、Over the last few years, Parland's commercial fishing enterprises have increased the number of fishing boats they use.
C、The main predator of these fish is another species of fish on which alligators also prey.
D、Many Parlanders who hunt alligators do so because of the high market price of alligator skins, not because of the threat alligators pose to the fish population.
E、In several neighboring countries through which Parland's rivers also flow, alligators are at risk of extinction as a result of extensive hunting.

答案:

C
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文章：

Technological improvements and reduced equipment costs have made converting solar energy directly into electricity far more cost-efficient in the last decade. However, the threshold of economic viability for solar power (that is, the price per barrel to which oil would have to rise in order for new solar power plants to be more economical than new oil-fired power plants) is unchanged at thirty-five dollars.

题目：

Which of the following, if true, does most to help explain why the increased cost-efficiency of solar power has not decreased its threshold of economic viability?

选项:

A、The cost of oil has fallen dramaticallyThe reduction in the cost of solar-power equipment has occurred despite increased raw material costs for that equipment
B、Technological changes have increased the efficiency of oil-fired power plants. 
C、Most electricity is generated by coal-fired or nuclear, rather than oil-fired, power plants.
D、When the price of oil increases, reserves of oil not previously worth exploiting become economically viable.

答案:

C
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题目：

Rainwater contains hydrogen of a heavy form called deuterium. The deuterium content of wood reflects the deuterium content of rainwater available to trees during their growth. Wood from trees that grew between 16,000 and 24,000 years ago in North America contains significantly more deuterium than wood from trees growing today. But water trapped in several North American caves that formed during that same early period contains significantly less deuterium than rainwater in North America contains today.

Which of the following, if true, most helps to reconcile the two findings?

选项:

A、There is little deuterium in the North American caves other than the deuterium in the water trapped there.
B、Exposure to water after a tree has died does not change the deuterium content of the wood.
C、Industrialization in North America over the past 100 years has altered the deuterium content of rain.
D、Trees draw on shallow groundwater from rain that falls during their growth, whereas water trapped in caves may have fallen as rainwater thousands of years before the caves formed.
E、Wood with a high deuterium content is no more likely to remain preserved for long periods than is wood with a low deuterium content.

答案:

D
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[Reading Comprehension]

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文章：

题目：

The passage provides information in support of which of the following assertions?

选项:

A、The disadvantages of an adaptation to a particular feature of an environment often outweigh the advantages of such an adaptation.
B、An organism's reaction to being placed in an environment to which it is not well adapted can sometimes illustrate the problems that have been solved by the adaptations of organisms indigenous to that environment.
C、The effectiveness of an organism's adaptation to a particular feature of its environment can only be evaluated by examining the effectiveness with which organisms of other species have adapted to a similar feature of a different environment.
D、Organisms of the same species that inhabit strikingly different environments will often adapt in remarkably similar ways to the few features of those environments that are common.
E、Different species of organisms living in the same environment will seldom adapt to features of that environment in the same way.

答案:

B
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题目：

Diabetes, together with its serious complications, ranks as the nation's third leading cause of death, surpassed only by heart disease and cancer.

选项:

A、ranks as the nation's third leading cause of death, surpassed only
B、rank as the nation's third leading cause of death, only surpassed
C、has the rank of the nation's third leading cause of death, only surpassed
D、are the nation's third leading causes of death, surpassed only
E、have been ranked as the nation's third leading causes of death, only surpassed

答案:

A
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题目：

Often patients with ankle fractures that are stable, and thus do not require surgery, are given follow-up x-rays because their orthopedists are concerned about possibly having misjudged the stability of the fracture. When a number of follow-up x-rays were reviewed, however, all the fractures that had initially been judged stable were found to have healed correctly. Therefore, it is a waste of money to order follow-up x-rays of ankle fractures initially judged stable.

Which of the following, if true, most strengthens the argument?

选项:

A、
A. Doctors who are general practitioners rather than orthopedists are less likely than orthopedists to judge the stability of an ankle fracture correctly.
B、
B. Many ankle injuries for which an initial x-ray is ordered are revealed by the x-ray not to involve any fracture of the ankle.
C、
C. X-rays of patients of many different orthopedists working in several hospitals were reviewed.
D、
D. The healing of ankle fractures that have been surgically repaired is always checked by means of a follow-up x-ray.
E、
E. Orthopedists routinely order follow-up x-rays for fractures of bones other than ankle bones.

答案:

C
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题目：

Economist: In 2015, the average per-person amount paid for goods and services purchased by consumers in Country X was the equivalent of $17,570 in United States dollars, just 30 percent of the corresponding figure of $58,566 for Country Y. Yet in 2015, there was already a substantial middle class in Country X that had discretionary income for middle-class consumer goods such as new vehicles, computers, or major household appliances, while a significant portion of the middle class in Country Y did not have sufficient income to purchase such items.

Which of the following, if true, most helps explain the discrepancy in the relationships described by the economist?

选项:

A、There are many consumer goods, such as household appliances, that are produced in Country X to be sold in the Country Y market.
B、The volume of trade between Country X and Country Y is increasing rapidly in both directions.
C、The economy of Country Y is recovering from a downturn that affected both Country Y and Country X.
D、Country X residents pay much less than their Country Y counterparts for housing, transportation, and child care.
E、In Country Y as well as in Country X, there are few assembly-line jobs in factories that pay a middle-class wage.

答案:

D
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题目：

Paper production accounts for approximately 40 percent of the world's industrial use of wood, and the market for paper is growing faster than it is for all major wood products.

选项:

A、 the market for paper is growing faster than it is for all
B、 the market for paper is growing faster than the market for all other
C、 the market for it is growing faster than it is for all other
D、 its market is growing faster than the market for all
E、 its market is growing faster than it is for all other

答案:

B
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题目：

Which of the following can be inferred from the passage concerning the environmentalists mentioned in line 8?

选项:

A、They are organized in opposition to the generation of income produced by the sale of ecological services.
B、They are fewer in number but better organized and better connected to the media than their opponents.
C、They have sometimes been charged with failing to use a particular strategy in their pursuit of conservational goals.
D、They have been in the forefront of publicizing the extent of worldwide environmental degradation.
E、They define environmental progress differently and more conservatively than do other organized groups of environmentalists.

答案:

C
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[Undefined]

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Art historian: Unlike many artistic traditions that sought to depict plants native to the local area in a seasonally appropriate way (for example, depicting scenes of spring with the plants in the appropriate stages of development for that season), seventeenth-century Dutch artists specializing in flower paintings almost exclusively chose to depict exotic species of flowers from outside the local area. Painting such species was worthwhile primarily because the art-buying public had developed a strong preference for images of the exotic. The great botanical centers of the time gave the artists direct access to such flowers, which the artists would freely combine in a single painting, regardless of whether the combined species occurred together in the wild, and depicted each in full bloom, regardless of whether those species bloomed at the same time in nature.

Statement: The art historian makes the point that the species of flowers these Dutch artists chose to paint were 1 largely because the species were 2 .

Select for 1 and for 2 the options that complete the statement so that it is most strongly supported by the information provided. Make only two selections, one in each column.
我选的CE，和EC有什么区别？怎么选出EC的？
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[Undefined]

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An unusually severe winter occurred in Europe after the continent was blanketed by a blue haze resulting from the eruption of the Laki Volcano in the European republic of Iceland in the summer of 1984.  Thus, it is evident that major eruptions cause the atmosphere to become cooler than it would be otherwise.
Which of the following statements, if true, most seriously weakens the argument above?
C选项为什么就不会有张冠李戴的问题呢，1984和1982的气候情况能一样吗，C里的火山就可以试用于原文的火山吗
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[Undefined]

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The rate of a certain chemical reaction is directly proportional to the square of the concentration of chemical A present and inversely proportional to the concentration of chemical B present. If the concentration of chemical B is increased by 100 percent, which of the following is closest to the percent change in the concentration of chemical A required to keep the reaction rate unchanged?
为什么这个题一定是相乘不能是相加呢？y=k1A方-k2B （k1,k2大于0 ），也满足题目说的与A方成正比与B成反比啊？但是这道题只有相乘的情况才能选出正确答案
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1038浏览

[Undefined]

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Tiger beetles are such fast runners that they can capture virtually any nonflying insect.  However, when running toward an insect, the beetles intermittently stop, and then, a moment later, resume their attack.  Perhaps they cannot maintain their pace and must pause for a moment's rest; but an alternative hypothesis is that while running tiger beetles are unable to process the resulting rapidly changing visual information, and so quickly go blind and stop.
 
Which of the following, if discovered in experiments using artificially moved prey insects, would support one of the two hypotheses and undermine the other?
答案C是怎么支持一个猜想又削弱另一个猜想的？
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2375浏览

[GWD]

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The author of the passage implies that which of the following is a possible partial explanation for acquisition behavior during the 1970's and 1980's?
请解释这道题为什么不选C或E，除了正确选项B，我认为文中也正确地提到了这两个选项可以解释acquisition behavior during 1970s and 80s
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[OG]

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The primary purpose of the passage is to
为什么选E不选B
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[Undefined]

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Club X has more than 10 but fewer than 40 members. Sometimes the members sit at tables with 3 members at one table and 4 members at each of the other tables, and sometimes they sit at tables with 3 members at one table and 5 members at each of the other tables. If they sit at tables with 6 members at each table except one and fewer than 6 members at that one table, how many members will be at the table that has fewer than 6 members?
提问小梅老师 这道题求讲一下 我没什么思路 带入数字得的是3
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A photography dealer ordered 60 Model X cameras to be sold for $250 each, which represents a 20 percent markup over the dealer's initial cost for each camera. Of the cameras ordered, 6 were never sold and were returned to the manufacturer for a refund of 50 percent of the dealer's initial cost. What was the dealer's approximate profit or loss as a percent of the dealer's initial cost for the 60 cameras?
请问小梅老师 这道题讲讲一下 我算的是19% 原来成本是200每个 亏了6个 每个亏100. 最后得不出答案
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[Undefined]

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Analytical!
请问may老师，这题该用什么思路来做？
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[Undefined]

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Analytical!
请问张老师，这道题为什么D不对？我有我觉得second paragraph最后一句话特别指向D
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