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1、精選優(yōu)質(zhì)文檔-傾情為你奉上Elements of LifeThe creation of life requires a set of chemical elements for making the components of cells. Life on Earth uses about 25 of the 92 naturally occurring chemical elements, although just 4 of these elements-oxygen, carbon, hydrogen, and nitrogen-make up about 96 percent of

2、the mass of living organisms. Thus, a first requirement for life might be the presence of most or all of the elements used by life. The word “components” in the passage is closest in meaning to· parts · bodies · combinations · characteristics Interestingly, this requirement can p

3、robably be met by almost any world. Scientists have determined that all chemical elements in the universe besides hydrogen and helium (and a trace amount of lithium) were produced by stars. These are known as heavy elements because they are heavier than hydrogen and helium. Although all of these hea

4、vy elements are quite rare compared to hydrogen and helium, they are found just about everywhere.According to paragraphs 1 and 2, living cells contain which of the following?· All chemical elements in the universe except lithium · About 25 different elements · About 96 percent of all

5、known elements · Ninety-two naturally occurring elements Heavy elements are continually being manufactured by stars and released into space by stellar deaths , so their amount compared to hydrogen and helium gradually rises with time. Heavy elements make up about 2 percent of the chemical conte

6、nt (by mass) of our solar system; the other 98 percent is hydrogen and helium. In some very old star systems, which formed before many heavy elements were produced, the heavy-element share may be less than 0.1 percent. Nevertheless , every star system studied has at least some amount of all the elem

7、ents used by life. Moreover, when planetesimals-small, solid objects formed in the early solar system that may accumulate to become planets-condense within a forming star system, they are inevitably made from heavy elements because the more common hydrogen and helium remain gaseous. Thus, planetesim

8、als everywhere should contain the elements needed for life, which means that objects built from planetesimals-planets, moons, asteroids, and comets-also contain these elements. The nature of solar-system formation explains why Earth contains all the elements needed for life, and it is why we expect

9、these elements to be present on other worlds throughout our solar system, galaxy, and universe. Why does the author provide the information that _ Heavy elements.stellar deaths _?· To explain how it is that the elements required for life can be found everywhere · To provide evidence that o

10、ur solar system is relatively young · To argue that some solar systems are more likely to support life than others · To explain why heavy elements have greater mass than hydrogen and helium ·Paragraph 3 suggests that which of the following may be a difference between very old star sys

11、tems and newer star systems?· Older star systems are likely to have fewer planets, moons, asteroids, and comets than newer star systems. · Newer star systems probably contain more hydrogen and helium than older star systems. · Newer star systems probably contain more heavy elements th

12、an older star systems. · The process of solar-system formation may have been fundamentally different in older star systems than in newer star systems. ·The word “Nevertheless” in the passage is closest in meaning to· additionally · however · in particular · on the contr

13、ary ·The word “inevitably” in the passage is closest in meaning to· typically · unsurprisingly · necessarily · naturally Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in

14、important ways or leave out essential information.· Planetesimals may remain in star systems when hydrogen and helium combine with less common heavier elements. · Planetesimals are composed of heavy elements because hydrogen and helium stay in the form of gases. · Planetesimals are sm

15、all, solid objects that condense within a forming star system and may become planets. · When planetesimals accumulate to form planets, they inevitably contain gaseous as well as heavy elements. Note that this argument does not change, even if we allow for life very different from life on Earth.

16、 Life on Earth is carbon based, and most biologists believe that life elsewhere is likely to be carbon based as well. However, we cannot absolutely rule out the possibility of life with another chemical basis, such as silicon or nitrogen. The set of elements (or their relative proportions) used by l

17、ife based on some other element might be somewhat different from that used by carbon-based life on Earth. But the elements are still products of stars and would still be present in planetesimals everywhere. No matter what kinds of life we are looking for, we are likely to find the necessary elements

18、 on almost every planet, moon, asteroid, and comet in the universe. According to paragraph 4, which of the following is true about possible life on other planets?· It cannot be based on silicon or nitrogen. · It could not survive on Earth. · It probably would not be made of elements p

19、roduced by stars. · It is likely to have carbon as its chemical basis. A somewhat stricter requirement is the presence of these elements in molecules that can be used as ready-made building blocks for life, just as early Earth probably had an organic soup of amino acids and other complex molecu

20、les. Earths organic molecules likely came from some combination of three sources: chemical reactions in the atmosphere, chemical reactions near deep-sea vents in the oceans, and molecules carried to Earth by asteroids and comets. The first two sources can occur only on worlds with atmospheres or oce

21、ans, respectively. But the third source should have brought similar molecules to nearly all worlds in our solar system. According to paragraph 5, all of the following are true of the organic molecules on early Earth EXCEPT:· Some of them were probably brought to Earth by asteroids or comets. &#

22、183; Some of them probably formed in the atmosphere and oceans. · They were probably significantly different from the organic molecules present on other planets in the solar system. · They included complex moleculesStudies of meteorites and comets suggest that organic molecules are widespr

23、ead among both asteroids and comets. Because each body in the solar system was repeatedly struck by asteroids and comets during the period known as the heavy bombardment (about 4 billion years ago), each body should have received at least some organic molecules. However, these molecules tend to be d

24、estroyed by solar radiation on surfaces unprotected by atmospheres. Moreover, while these molecules might stay intact beneath the surface (as they evidently do on asteroids and comets), they probably cannot react with each other unless some kind of liquid or gas is available to move them about. Thus

25、, if we limit our search to worlds on which organic molecules are likely to be involved in chemical reactions, we can probably rule out any world that lacks both an atmosphere and a surface or subsurface liquid medium, such as water. The phrase “widespread among” is closest in meaning to· frequ

26、ently present in · widely separated in · a significant part of · found throughout the bodies of The Commercialization of LumberIn nineteenth-century America, practically everything that was built involved wood. Pine was especially attractive for building purposes. It is durable and st

27、rong, yet soft enough to be easily worked with even the simplest of hand tools. It also floats nicely on water, which allowed it to be transported to distant markets across the nation. The central and northern reaches of the Great Lakes states-Michigan, Wisconsin, and Minnesota-all contained extensi

28、ve pine forests as well as many large rivers for floating logs into the Great Lakes, from where they were transported nationwide. The word “durable ” in the passage is closest in meaning to· readily available · long lasting · dense · flexible According to paragraph 1, all of the

29、following characteristics of pine made it a desirable material for building in nineteenth-century America EXCEPT:· It was long lasting. · It was relatively easy to transport. · Its softness made it easy to work with. · It produced buildings that were especially attractive. By 186

30、0, the settlement of the American West along with timber shortages in the East converged with ever-widening impact on the pine forests of the Great Lakes states. Over the next 30 years, lumbering became a full-fledged enterprise in Michigan, Wisconsin, and Minnesota. Newly formed lumbering corporati

31、ons bought up huge tracts of pineland and set about systematically cutting the trees. Both the colonists and the later industrialists saw timber as a commodity , but the latter group adopted a far more thorough and calculating approach to removing trees. In this sense, what happened between 1860 and

32、 1890 represented a significant break with the past. No longer were farmers in search of extra income the main source for shingles, firewood, and other wood products. By the 1870s, farmers and city dwellers alike purchased forest products from large manufacturing companies located in the Great Lakes

33、 states rather than chopping wood themselves or buying it locally. The word “commodity ” in the passage is closest in meaning to· product · problem · opportunity · advantage What can be inferred from paragraph 2 about timber in America before the year 1860 ?· Farmers of the

34、American West earned most of their income by selling timber to newly arrived settlers. · Timber came primarily from farmers who wished to supplement their income. · Timber was much more expensive before the year 1860 because it was less readily available. · Timber came primarily from

35、large manufacturing companies in the EastThe commercialization of lumbering was in part the product of technological change. The early, thick saw blades tended to waste a large quantity of wood, with perhaps as much as a third of the log left behind on the floor as sawdust or scrap. In the 1870s, ho

36、wever, the British-invented band saw , with its thinner blade, became standard issue in the Great Lakes states lumber factories. Meanwhile, the rise of steam-powered mills streamlined production by allowing for the more efficient, centralized, and continuous cutting of lumber. Steam helped to automa

37、te a variety of tasks, from cutting to the carrying away of waste. Mills also employed steam to heat log ponds, preventing them from freezing and making possible year-round lumber production. Why does the author discuss the “British-invented band saw ”?· To give an example of how steam power le

38、d to technological advancements · To help explain how the thickness of a saw blade determines how much wood is wasted · To explain how competition with other countries benefited the American lumber industry · To illustrate the impact of new technology on the lumber industry The phrase

39、 “allowing for ” in the passage is closest in meaning to· encouraging · introducing · making possible · emphasizing All of the following are mentioned in paragraph 3 as resulting from the use of steam in the lumber industry EXCEPT:· Work became centralized, and many tasks we

40、re automated. · Lumber could be produced more efficiently and on a larger scale. · Waste materials could be re-used as fuel to power the lumber mills. · Lumber production could continue throughout the cold winter monthsFor industrial lumbering to succeed, a way had to be found to neut

41、ralize the effects of the seasons on production. Traditionally, cutting took place in the winter, when snow and ice made it easier to drag logs on sleds or sleighs to the banks of streams. Once the streams and lakes thawed, workers rafted the logs to mills, where they were cut into lumber in the sum

42、mer. If nature did not cooperate-if the winter proved dry and warm, if the spring thaw was delayed-production would suffer. To counter the effects of climate on lumber production, loggers experimented with a variety of techniques for transporting trees out of the woods. In the 1870s, loggers in the

43、Great Lakes states began sprinkling water on sleigh roads, giving them an artificial ice coating to facilitate travel. The ice reduced the friction and allowed workers to move larger and heavier loads. The word “facilitate ” in the passage is closest in meaning to· expand · ease · tra

44、nsform · permit According to paragraph 4, how could a warm, dry winter interfere with lumber production?· Certain trees would become dry and yield low-quality lumber. · There would not be enough water in streams and lakes to raft the logs to mills. · It would be more difficult to

45、 transport logs to streams and lakes. · Rivers would not be full enough in the spring to power millsBut all the sprinkling in the world would not save a logger from the threat of a warm winter. Without snow the sleigh roads turned to mud. In the 1870s, a set of snowless winters left lumber comp

46、anies to ponder ways of liberating themselves from the seasons. Railroads were one possibility. At first, the remoteness of the pine forests discouraged common carriers from laying track. But increasing lumber prices in the late 1870s combined with periodic warm, dry winters compelled loggers to tur

47、n to iron rails. By 1887, 89 logging railroads crisscrossed Michigan, transforming logging from a winter activity into a year-round one. The word “remoteness ” in the passage is closest in meaning to· decline · density · size · isolation Once the logs arrived at a river, the trip

48、 downstream to a mill could be a long and tortuous one. Logjams (buildups of logs that prevent logs from moving downstream) were common-at times stretching for 10 miles-and became even more frequent as pressure on the northern Midwest pinelands increased in the 1860s. To help keep the logs moving ef

49、ficiently, barriers called booms (essentially a chain of floating logs) were constructed to control the direction of the timber. By the 1870s, lumber companies existed in all the major logging areas of the northern Midwest. Overkill of the North American MegafaunaThousands of years ago, in North Ame

50、ricas past, all of its megafauna-large mammals such as mammoths and giant bears-disappeared. One proposed explanation for this event is that when the first Americans migrated over from Asia, they hunted the megafauna to extinction. These people, known as the Clovis society after a site where their d

51、istinctive spear points were first found, would have been able to use this food source to expand their population and fill the continent rapidly. Yet many scientists argue against this "Pleistocene (the period between about 2.5 million and 11,700 years ago during which humans first appeared on

52、Earth) overkill" hypothesis. Modern humans have certainly been capable of such drastic effects on animals, but could ancient people with little more than stone spears similarly have caused the extinction of numerous species of animals? Thirty-five genera or groups of species (and many individua

53、l species) suffered extinction in North America around 11,000 B.C., soon after the appearance and expansion of Paleo-Indiansa group of hunters active in America during the late Pleistocene throughout the Americas (27 genera disappeared completely, and another 8 became locally extinct, surviving only

54、 outside North America). The word “proposed” in the passage is closest in meaning to· accepted · obvious · debatable · suggested The word “distinctive ” in the passage is closest in meaning to· hidden · characteristic · scattered · rare Why does the author com

55、pare “Modern humans” with “ancient people”?· To argue that modern people have continued to have drastic effects on animal species · To illustrate how people from different historical times treated animals differently · To question the idea that ancient people could have hunted the meg

56、afauna to extinction · To emphasize that modern people are more successful hunters than ancient people were Although the climate changed at the end of the Pleistocene, warming trends had happened before. A period of massive extinction of large mammals like that seen about 11,000 years ago had n

57、ot occurred during the previous 400,000 years, despite these changes. The only apparently significant difference in the Americas 11,000 years ago was the presence of human hunters of these large mammals. Was this coincidence or cause-and-effect?We do not know. Ecologist Paul S. Martin has championed

58、 the model that associates the extinction of large mammals at the end of the Pleistocene with human predation. With researcher J. E. Mosimann, he has co-authored a work in which a computer model showed that in around 300 years, given the right conditions, a small influx of hunters into eastern Berin

59、gia 12,000 years ago could have spread across North America in a wave and wiped out game animals to feed their burgeoning population. In using the word “coincidence ” in the passage, the author refers to events that occurred· after a period of many years · subsequent to a prediction ·

60、 from time to time · at the same time and by chance According to paragraph 2, what suggests that human activity played a role in the extinction of mammals about 11,000 years ago?· Climate changes that would have favored human population expansion occurred at the time of the extinctions. · The presence of human hunters had caused animal extinctions in other time periods.