The idea of naturalselectionis that organisms in aspeciesthat have characteristics favoringsurvivalare most likely tosurviveand produceoffspringwith the same characteristics. Because thesurvivalof organisms withparticularcharacteristics isfavoredover thesurvivalof other organisms in the samespeciesthatlackthese characteristics, future generations of thespeciesare likely to include more organisms with thefavorablecharacteristics.

One of the most thoroughly analyzed examples of naturalselectionin operation is the change in color that has occurred in certain populations of the pepperedmoth, Biston betularia, inindustrialregions of Europe during the past 100 years. Originally moths wereuniformlypalegray or whitish in color; dark-colored (melanic) individuals wererareand made up less than 2 percent of thepopulation. Over a period of decades, dark-colored forms became an increasingly largefractionof some populations andeventuallycame todominatepepperedmothpopulations in certain areas —especially those ofextremeindustrializationsuch as the RuhrValleyof Germany and the Midlands of England. Coalfromindustryreleased large amounts of blacksootinto the environment, but the increase of the dark-colored forms was notduetogeneticmutations caused byindustrialpollution. For example, caterpillars that feed on soot-covered leaves did not give rise to dark- colored adults. Rather, pollution promoted thesurvivalof dark forms on soot-covered trees. Melanics werenormallyquickly eliminated in nonindustrial areas byadverseselection; birds spotted them easily. Thisphenomenon, an increase in thefrequencyof dark-colored mutants in polluted areas, is known asindustrialmelanism. The North Americanequivalentof this story is anothermoth, the swettaria form of Biston cognataria, first noticed in industrialized areas such as Chicago and New York City in the early 1900s. By 1961 it constituted over 90 percent of thepopulationin parts of Michigan.

The idea that naturalselectionwasresponsiblefor the changingratioof dark- to light-colored peppered moths was developed in the 1950s by H. B. D. Kettlewell of Oxford University. If naturalselectionwas the explanation, then there should be differentsurvivalrates for dark- and light- colored moths. Todeterminewhether this was true, Kettlewell released thousands of light and dark moths (eachmarkedwith a paintspot) intoruraland industrialized areas. In the nonindustrial area of Dorset, he recaptured 14.6 percent of thepaleforms but only 4.7 percent of the dark forms. In theindustrialarea of Birmingham, the situation was reversed: 13 percent ofpaleforms but 27.5 percent of dark forms were recaptured.

Clearly someenvironmentalfactorwasresponsiblefor the greatersurvivalrates of dark moths. Birds were predators of peppered moths. Kettlewell hypothesized that the normalpaleforms are difficult to see when resting on lichen-covered trees, whereas dark forms areconspicuous. In industrialized areas, lichens are destroyed by pollution, tree barks become darker, and dark moths are the ones birds have difficulty detecting. As a test, Kettlewell set up hiddenobservationpositions and watched birdsvoraciouslyeat moths placed |on tree trunks of a contrasting color. Theactionof naturalselectionin producing a small but highlysignificantstep ofevolutionwas seemingly demonstrated, with birds as the selecting force.

Not every researcher has been convinced that naturalselectionby birds is the only explanation of the observed frequencies of dark and light peppered moths. More recentdata, however, provideadditionalsupport for Kettleweir's ideas about naturalselection. The light-colored form of the pepperedmothis making a strong comeback. In Britain, a CleanAirAct was passed in 1965. Sir Cyril Clarke has been trapping moths at his home in Liverpool, Merseyside, since 1959. Before about 1975, 90 percent of the moths were dark, but since then there has been asteepdeclinein melanic forms, and in 1989 only 29.6 percent of the moths caught were melanic. The meanconcentrationof sulphurdioxidepollution fell from about 300 micrograms per cubic meter in 1970 to less than 50 micrograms per cubic meter in 1975 and has remainedfairlyconstantsince then. If thespreadof the light-colored form of themothcontinues at the same speed as the melanic formspread.in the lastcentury, soon the melanic form will again be only anoccasionalresidentof the Liverpool area.

Questions:
question_stem: 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.
choices: tag: A
text: Peppered moth populations gradually increased in size, with dark-colored moths increasing their numbers fastest in the industrialized areas of Germany and England.

tag: B
text: Over a period of decades, dark-colored peppered moths came to certain areas of the Ruhr Valley and the Midlands and became the dominant forms there.

tag: C
text: In Germany and England, dark-colored peppered moths forced most light-colored moths out of their territories.

tag: D
text: While they also increased elsewhere, dark-colored peppered moths gradually became the dominant form in areas of extreme industrialization.
answer_key: D
explanation: 本题所说高亮部分定位在这里：Over a period of decades, dark-colored forms became an increasingly large fraction of some populations and eventually came to dominate peppered moth populations in certain areas —especially those of extreme industrialization such as the Ruhr Valley of Germany and the Midlands of England. 这句话的大意是黑色的蛾子在所有蛾子中所占比例逐渐加大，进而在某些地区成为了优势物种，特别是在有大型工业的地区。选项 D 是这句话的同义转述，选择；选项 A 是说这种黑色蛾子在英国和德国工业地区数量增长最快，原文里并没有提，错误；选项 B 是说黑色蛾子来到了两个工业地区，并快速繁殖，占领优势地位，因果关系错误；选项 C 是说黑色蛾子把浅色蛾子赶走了，原文里也没有说。选择 D。

question_stem: In the passage, why does the author mention that "the increase of the dark-colored forms was not due to genetic mutations caused by industrial pollution"?
choices: tag: A
text: To suggest that the rate of genetic change in peppered moths actually decreased.

tag: B
text: To emphasize that pollution in industrial areas had no role in the increase of dark peppered moths.

tag: C
text: To introduce the information about the soot-covered trees that caterpillars fed on as the correct explanation for the increase in dark peppered moths.

tag: D
text: To reject a view of the role of pollution in the increase of dark peppered moths that would not involve natural selection.
answer_key: D
explanation: 根据题干给的句子定位到原文这一句：Coal from industry released large amounts of black soot into the environment, but the increase of the dark-colored forms was not due to genetic mutations caused by industrial pollution. 这句话的大意是，工业生产上燃烧的煤炭的确会像自然界排放黑的污染，但是黑色蛾子的增加并不是这种污染大量排放导致的基因突变。后半句话旨在反驳前半句提出的理论，即选项 D 所说的内容。选项 A 说蛾子里基因变化的频率下降了，选项 B 说的是污染跟蛾子的变异没有关系，这个太绝对，文章里并没有提，不选；选项 C 是关于被污染的树和以它们为生的蛾子的，这个原文里也没有。选择 D。

question_stem: The phrase "give rise to" in the passage is closest in meaning to
choices: tag: A
text: live longer than

tag: B
text: associate with

tag: C
text: produce

tag: D
text: compete with
answer_key: C
explanation: 根据所考察词汇 give rise to 定位到原文中的 For example, caterpillars that feed on soot-covered leaves did not give rise to dark- colored adults. 这句话的大意是：例如，以被煤灰覆盖的树叶为食的毛毛虫并没有长成黑色的成虫。这里 give rise to 是长成，变成的意思。选项 A 是比……活得长，选项 B 是与……有关系，选项 C 是产生，选项 D 是与……竞争。选项 C 最贴近 give rise to 的意思。选择 C。

question_stem: The passage suggests which of the following about "the swettaria form of Biston cognataria"?
choices: tag: A
text: It was a dark-colored moth form.

tag: B
text: It is now extinct in industrialized areas.

tag: C
text: It did not exist before the early 1900s.

tag: D
text: It came to North America from Europe.
answer_key: A
explanation: 根据题干中给出的 the swettaria form of Biston cognataria 定位到原文中这一句：The North American equivalent of this story is another moth, the swettaria form of Biston cognataria, first noticed in industrialized areas such as Chicago and New York City in the early 1900s. 这句话的大意是，在北美也有另一种蛾子，是 Biston cognataria 的 swettaria form，这一种蛾子也是最先在20世纪初期在工业化的地区比如芝加哥和纽约发现的。通过这一句的措辞 equivalent，即等价物我们可以知道，这句话讲的是与前文的黑色蛾子相同的一个现象。所以两处的蛾子都是黑的，A 选项正确。至于其余三个选项，原文中都没有提及。

question_stem: Paragraph 3 answers all of the following questions about Kettlewell's experiment EXCEPT:
choices: tag: A
text: How was it determined whether a recaptured moth was one of those that Kettlewell released?

tag: B
text: Were equal numbers of dark-and light-colored moths released?

tag: C
text: What hypothesis was Kettlewell trying to test with the experiment?

tag: D
text: What were the results of the experiment?
answer_key: B
explanation: 本题的关键词是 Kettlewell 和 experiment。根据关键词定位回第三段，通读这一段我们发现，Kettlewell 这个实验过程是这样的：他先把相同数量的黑蛾子和浅色蛾子做上标记，然后分别在工业地区和非工业地区放生，过一段时间再捕获它们，统计两种蛾子的数量。选项 A 说怎么确定捕捉到的蛾子是以前放生的，这个可以通过标记来识别；选项 B 问两种颜色的蛾子放生的数量是不是一样的，这个实验没有说明，只是说放了上千只的蛾子，但是具体那种放了多少并没有说；选项 C 说想证明什么假设，本段第一句就是说的这个要证明的假设，正确；选项 D 是说实验的结果，这个在本段最后也给出了。选择 B。

question_stem: The word "conspicuous" in the passage is closest in meaning to
choices: tag: A
text: easily eaten

tag: B
text: clearly visible

tag: C
text: poorly adapted

tag: D
text: rarely present
answer_key: B
explanation: 根据本题所考察的词汇定位到这一句：Kettlewell hypothesized that the normal pale forms are difficult to see when resting on lichen-covered trees, whereas dark forms are conspicuous. 本句的大意是 Kettlewell 假设说正常的白蛾子趴在青苔覆盖的树干上很难被发现，但是黑的蛾子就特别明显了。conspicuous 意思是显而易见的。选项 A 是说容易被吃掉的，选项 B 是说看得很清楚的，选项 C 是说没有改进的，选项 D 是说很少出现的。选项 B 最贴合 conspicuous 的意思。选 B。

question_stem: Paragraph 4 suggests which of the following about the survival of peppered moths?
choices: tag: A
text: Light forms of the moth are more likely to survive in polluted rather than unpolluted areas.

tag: B
text: Birds are more likely to determine the survival rates of moths in rural rather than industrial areas.

tag: C
text: Environment determines whether dark or light forms of the moth survive.

tag: D
text: The presence of lichen on tree trunks encourages birds to prey on both dark and light forms of the moth with the same frequency.
answer_key: C
explanation: 本题题干给的关键词是 the survival of peppered moths。回看第四段发现整段都在讲 peppered moths 的生存问题。这一段的主要内容是：鸟类是帮助蛾子进化的助力，因为鸟类更容易吃到在树干上显得很显眼的蛾子。所以青苔上的黑蛾子、煤炭熏过地方的白蛾子都是容易被吃掉的，相反则容易存活。所以是环境决定了那种颜色的蛾子容易活下去，选项 C 符合题意。选项 A 说浅色蛾子更容易在被工业污染地区活下去，与原文相悖；选项 B 说鸟类更容易决定乡村蛾子的存活而不是工业化地区的，这个原文里没有提及；选项 D 说青苔同时促进了鸟类捕食浅色蛾子和黑色蛾子，错误，是只促进了鸟类捕食黑色蛾子。选择 C。

question_stem: The word "detecting" in the passage is closest in meaning to
choices: tag: A
text: discovering

tag: B
text: capturing

tag: C
text: eating

tag: D
text: hiding
answer_key: A
explanation: 根据本题所考察的词汇定位到这一句：In industrialized areas, lichens are destroyed by pollution, tree barks become darker, and dark moths are the ones birds have difficulty detecting. 本句大意是：在工业化地区，青苔被破坏，树被煤烟熏黑，黑蛾子变成了不容易被发现的那种蛾子。detecting 在这里的意思是被发现。选项 A 的意思是被发现，选项 B 的意思是被捕获，选项 C 的意思是被吃掉，选项 D 的意思是被藏起来。选项 A 最贴合 detecting 的意思。选择 A。

question_stem: The word "convinced" in the passage is closest in meaning to
choices: tag: A
text: persuaded

tag: B
text: concerned

tag: C
text: informed

tag: D
text: pleased
answer_key: A
explanation: 根据本题所考察的词汇定位到这一句：Not every researcher has been convinced that natural selection by birds is the only explanation of the observed frequencies of dark and light peppered moths. 本句大意是：并不是每一个研究者都相信，由鸟类进行的自然选择是黑蛾子和浅色蛾子的数量变化的唯一解释。convince 在这里的意思是使相信。选项 A 的意思是说服，选项 B 的意思是关心，选项 C 的意思是通知，选项 D 的意思是取悦。选项 A 最贴合 convince 的意思。选择 A。

question_stem: What is the purpose of paragraph 5 in the passage?
choices: tag: A
text: To explain why Kettlewell's view has been widely misunderstood.

tag: B
text: To present a view that various researchers have criticized.

tag: C
text: To suggest why new developments seem to confirm Kettlewell's view.

tag: D
text: To state one of the proposed alternatives to Kettlewell's view.
answer_key: C
explanation: 一般而言，托福文章的第一句就是本段的主旨句。本题可以通过读第五段的第一句来得到结论。Not every researcher has been convinced that natural selection by birds is the only explanation of the observed frequencies of dark and light peppered moths. More recent data, however, provide additional support for Kettleweir's ideas about natural selection.本句意为并不是所有的研究者相信鸟的自然选择一说是蛾子种类数量变化的唯一解释，而且还有更多最近的数据支持了 Kettleweir 的理论。也就是说下文会详细说明这些数据是怎么证明 Kettleweir 的理论的。选项 A 说为了解释为什么 K 的理论会被误解，选项 B 说为了说明一个被研究者们批判的理论，选项 C 说为了说明为什么新的发现会支持 K 的理论，选项 D 说为了说明 K 的理论的变化之一。只有 C 最符合第五段内容。选择 C。

question_stem: According to paragraph 5, which of the following is true of melanic forms in Liverpool?
choices: tag: A
text: Increased sulphur dioxide pollution decreased their numbers after 1975.

tag: B
text: Their population slowly increased from 1975 to 1989.

tag: C
text: From 1950 on, they have seldom been seen in the Liverpool area.

tag: D
text: Before 1975 their population was higher than that of light-colored moths.
answer_key: D
explanation: 本题以 Liverpool 为关键词定位：In Britain, a Clean Air Act was passed in 1965. Sir Cyril Clarke has been trapping moths at his home in Liverpool, Merseyside, since 1959. 这一句以及下面的句子都与本题相关。这一部分的大意是：一开始百分之九十的蛾子是黑的，但是以后随时间的推移黑蛾子越来越少，少到了不到百分之三十。同时，这个地区的硫的含量也在下降。选项 A 是说增加的二氧化硫导致了黑蛾子的减少，这个文章中没有提到；选项 B 是说这些蛾子的数量从1975到1989在增加，不对，应该是减少；选项 C 是说从1950年开始，黑蛾子就很少被看见了，这个也不对，黑蛾子没有减少到这么少；选项 D 是说1975年以前黑蛾子比浅蛾子多，是对的，因为1975年以前黑蛾子占90%，浅蛾子占10%，黑多于白。选择 D。

question_stem: In paragraph 5 the change in the frequency of melanic forms is attributed to which of the following?
choices: tag: A
text: New kinds of pollution in Liverpool

tag: B
text: The passage of the Clean Air Act in 1965

tag: C
text: Changes in rates of genetic mutation

tag: D
text: Changes in populations of moth predators
answer_key: B
explanation: 这一题问的是导致黑蛾子数量变化的原因。根据对上一题的分析，我们知道因为 a Clean Air Act 的通过导致了空气里的硫的减少，伴随着黑蛾子数量减少和浅色蛾子数量增多。所以可以推理出作者应该是想说明工业污染影响蛾子种类的数量。选项 B 符合题意。选项 A 说的是新的污染，这个文中没有提到；选项 C 是说基因突变的速率，没有提到；选项 D 是说蛾子的捕食者的数量变化，也没有提到。选择 B。