介词短语做后置定语。如lava on the surface，中 on the surface介词短语修饰lava，表示为表面上的熔岩。
现在分词短语做后置定语。如the blood vessels carrying cooled blood.中的carrying cooled blood就是现在分词短语用来修饰限定the blood vessels，理解为运载着凉的血液的血管。
过去分词短语做后置定语，the gradual drying of the soil caused by its diminished ability中的caused by its diminished ability就是过去分词短语做后置定语修饰the gradual drying of the soil，理解为减少的能力导致的土壤的干燥。
不定式短语做后置定语。the ability to absorb water中to absorb water限定修饰 the ability，理解为吸收水的能力。
托福阅读TPO31第1篇:Speciation in Geographically Isolated Populations
【1】Evolutionary biologists believe that speciation, the formation of a new species, often begins when some kind of physical barrier arises and divides a population of a single species into separate subpopulations. Physical separation between subpopulations promotes the formation of new species because once the members of one subpopulation can no longer mate with members of another subpopulation, they cannot exchange variant genes that arise in one of the subpopulations. In the absences of gene flow between the subpopulations, genetic differences between the groups begin to accumulate. Eventually the subpopulations become so genetically distinct that they cannot interbreed even if the physical barriers between them were removed. At this point the subpopulations have evolved into distinct species. This route to speciation is known as allopatry (“alio-” means “different”，and “patria” means “homeland”).
【2】Allopatric speciation may be the main speciation route. This should not be surprising, since allopatry is pretty common. In general, the subpopulations of most species are separated from each other by some measurable distance. So even under normal situations the gene flow among the subpopulations is more of an intermittent trickle than a steady stream. In addition, barriers can rapidly arise and shut off the trickle. For example, in the 1800s a monstrous earthquake changed the course of the Mississippi River, a large river flowing in the central part of the United States of America. The change separated populations of insects now living along opposite shore, completely cutting off gene flow between them.
【3】Geographic isolation also can proceed slowly, over great spans of time. We find evidence of such extended events in the fossil record, which affords glimpses into the breakup of formerly continuous environments. For example, during past ice ages, glaciers advanced down through North America and Europe and gradually cut off parts of populations from one another. When the glacier retreated, the separated populations of plants and animals came into contact again. Some groups that had descended from the same parent population were no longer reproductively compatible—they had evolved into separate species. In other groups, however, genetic divergences had not proceeded so far, and the descendants could still interbreed—for them, reproductive isolation was not completed, and so speciation had not occurred.
【4】Allopatric speciation can also be brought by the imperceptibly slow but colossal movements of the tectonic plates that make up Earth’s surface. About 5 million years ago such geologic movements created the land bridge between North America and South America that we call the Isthmus of Panama. The formation of the isthmus had important consequences for global patterns of ocean water flow. While previously the gap between the continents had allowed a free flow of water, now the isthmus presented a barrier that divided the Atlantic Ocean from the Pacific Ocean. This division set the stage for allopatric speciation among populations of fishes and other marine species.
【5】In the 1980s, John Graves studied two populations of closely related fishes, one population from the Atlantic side of isthmus, the other from the Pacific side. He compared four enzymes found in the muscles of each population. Graves found that all four Pacific enzymes function better at lower temperatures than the four Atlantic versions of the same enzymes. This is significant because Pacific seawater is typically 2 to 3 degrees cooler than seawater on the Atlantic side of isthmus. Analysis by gel electrophoresis revealed slight differences in amino acid sequence of the enzymes of two of the four pairs. This is significant because the amino acid sequence of an enzyme is determined by genes.
【6】Graves drew two conclusions from these observations. First, at least some of the observed differences between the enzymes of the Atlantic and Pacific fish populations were not random but were the result of evolutionary adaption. Second, it appears that closely related populations of fishes on both sides of the isthmus are starting to genetically diverge from each other. Because Graves’s study of geographically isolated populations of isthmus fishes offers a glimpse of the beginning of a process of gradual accumulation of mutations that are neutral or adaptive, divergences here might be evidence of allopatric speciation in process.
托福阅读TPO31试题第1篇:Speciation in Geographically Isolated Populations
1.The word "promotes" in the passage is closest in meaning to
2.According to paragraph 1, allopatric speciation involves which of the following?
A.The division of a population into subspecies.
B.The reuniting of separated populations after they have become distinct species.
C.The movement of a population to a new homeland.
D.The absence of gene flow between subpopulations.
3.Why does the author provide the information that "the subpopulations of most species are separated from each other by some measurable distance"?
A.To indicate how scientists are able to determine whether subpopulations of a species are allopatric.
B.To define what it means for a group of animals or plants to be a subpopulation.
C.To suggest that allopatric speciation is not the only route to subpopulation.
D.To help explain why allopatric speciation is a common way for new species to come about.
4.The word "accumulate" in the passage is closest in meaning to
A.Become more significant.
C.Gradually increase in number.
5.In paragraph 2,why does the author mention that some insect populations were separated from each other by a change in the course of Mississippi River caused by an earthquake?
A.To make the point that some kind of physical barrier separates the subpopulations of most species.
B.To support the claim that the condition of allopatry can sometimes arise in a short time.
C.To provide an example of a situation in which gene flow among the subpopulations of a species happens at a slow rate.
D.To explain why insects living along opposite shores of the Mississippi River are very different from each other.
6.According to paragraph 3，separation of subpopulations by glaciers resulted in speciation in those groups of plants and animals that
A.were reproductively isolated even after the glaciers disappeared.
B.had adjusted to the old conditions caused by the glaciers.
C.were able to survive being separated from their parent population.
D.had experienced some genetic divergences from their parent population.
7.The word "colossal" in the passage is closet in meaning to
8.According to paragraph 4, which of the following is true of the geologic movements that brought about the Isthmus of Panama?
A.The movements brought populations of certain fishes and marine organisms into contact with one another for the first time.
B.The movements transferred populations of fishes and other marine animals between the Pacific and Atlantic Oceans.
C.The movements created conditions that allowed water to flow more freely between the Pacific and Atlantic Oceans.
D.The movements created conditions for the formation of new species of fishes and other marine animals.
9.The word "sequence" in the passage is closet in meaning to
10.According to paragraph 5, by comparing the enzymes from two related groups of fishes on opposite sides of the isthmus, Graves found evidence that
A.there were slight genetic divergences between the two groups.
B.the Atlantic group of fishes were descended from the Pacific group of fishes.
C.the temperature of water on either side of the isthmus had changed.
D.genetic changes in the Atlantic group of fishes were more rapid and frequent than in the Pacific group of fishes.
11.It can be inferred from paragraph 5 and 6 that the reason Graves concluded that some of the differences between the Pacific and Atlantic enzymes were not random was that
A.each of the Pacific enzymes works better in cooler waters.
B.the Enzymes of the Atlantic fish populations had not changed since the formation of the Isthmus of Panama.
C.gel electrophoresis showed that the changes benefited both the Atlantic and the Pacific fish populations.
D.the differences between the enzymes disappeared when the two fish populations were experimentally switched to other side of the isthmus.
12.Which of the sentence 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.Graves's study provides evidence that isthmus fishes are in the process of becoming geographically isolated.
B.Graves's study of mutating isthmus fishes yields results that differ from results of other studies involving allopatric speciation.
C.Graves's study of isolated populations of isthmus fishes provides some evidence that allopatric speciation might be beginning
D.Grave's study indicates that when isolated, populations of isthmus fished register neutral or adaptive mutations.
13. Look at the four squares [■] that indicate where the following sentence can be added to the passage.Where would the sentence best fit? The formation of the isthmus had important consequences for global patterns of ocean water flow.
Allopatric speciation can also be brought by the imperceptibly slow but colossal movements of the tectonic plates that make up Earth's surface. ■【A】 About 5 million years ago such geologic movements created the land bridge between North America and South America that we call the Isthmus of Panama. The formation of the isthmus had important consequences for global patterns of ocean water flow. ■【B】 While previously the gap between the continents had allowed a free flow of water, now the isthmus presented a barrier that divided the Atlantic Ocean from the Pacific Ocean. ■【C】This division set the stage for allopatric speciation among populations of fishes and other marine species. ■【D】
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 sentences do not belong in the summary because they express ideas that are not presented in the passages or are minor ideas in the passage. This question is worth 2 points.
Allopatric speciation takes place when physically separated populations of a single species gradually diverge genetically to the point of becoming unable to interbreed
A.Allopatric speciation is common because the gene flow between subpopulations is generally limited and the barriers that completely separate subpopulations can arise in a variety of ways.
B.During past ice ages, some, but not all, subpopulations separated by glaciers evolved into distinct species.
C.Speciation does not need to take place through allopatry because subpopulations will form distinct species whenever there are adaptive advantages or not
D.Physical barriers from glaciers and the movement of tectonic plates form so slowly that the subpopulations on either side of the barriers usually do not form distinct species.
E.Graves's study of fish populations separated by the Isthmus of Panama may well provide a picture of the beginning stages of speciation.
F.Graves's study of physically separated fish populations show that there must be large differences between the environments of the isolated populations if allopatric speciation is to take place.
托福阅读TPO31答案第1篇:Speciation in Geographically Isolated Populations
1.promote本身是促进的意思。另外原文这个句子意思是subpopulations间的物理分割...了新物种的形成，A描 述，B促使，C减弱，D要求。 所以B最合适的。
2.根据allopatric进行定位，可定位至本段的最后一句。最后一句是对前面现象的一个命名和定义。也就是说前 面的内容，就是allopatry的意 思。A与原文不附，原文说的 是物理 barrier 把 population 分割成 subpopulation，B 也不对， 对应Eventually这句。C原文没提到。D正确，对应从In the absence开始到最后。
3.高亮句前面的一句话，也就是本段的第一句(主旨句)，allopatry是main speciation route。本段都是围绕着这个主题来进行的。所以选择D。
4.词汇所在句说群落间基因的区别开始accumulate。 Eventually对理解这个词很有 帮助，也就是说是渐渐发展的，才能说最终。所以答案在A，C之间。但因为这里强调了缓慢的过 程，gradually更合适。
5.For example后面就是题目中的内容，那么也就是说作者用此作为例子来支持前 面的观点。而前面的观点是 barriers也有可能突然发生，然后截断了这种trickle。所以对应的是B。
6.根据Glaciers 和 plants and animals定位，可得知这是glacier separation 导致的结果。所以对应选项A。
7.Colossal本身是巨大的， 非常的意思，这里对应C选项。分析原文也可以得到正确答案，与colossal并列的词汇是slow，中间的逻辑关系词 是but,证明两者有转折关系。再经过推断，缓慢的过程但量 大的话就足以发生巨大的改变。所以选C。
8.根据 Isthmus of Panama 定位。从About开始。本段的 最后一句说了isthmus of Panama带来的结果，对应了D选项。
11.A对应了标注句子，B明显错误，文章一直在说改变。C文章提到 gel electrophoresis的地方只是说氨基酸的顺序改变，但没说both benefited。D文章也没提到。
13.要插入的句子提到了 formation of the isthmus，那么证明句子前面的内容中己经出现了isthmus，而后面则是 要说明consequences。第二个空符合逻辑，所以选择B。