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第一篇

Black Holes Trigger Stars to Self-Destruct

Scientists have long understood that supermassive black holes weighing millions or billions of suns can tear apart stars that come too close. The black hotels gravity pulls harder on the nearest part of the star, an imbalance that pulls the star apart over a period of minutes or hours, once it gets close enough.

Scientists say this Uneven pulling is not the only hazard facing the star. The strain of these unbalanced forces can also trigger a nuclear explosion powerful enough to destroy the star from within. Matthieu Brassart and Jean-Pierre Luminet of the Observatoire de Paris in Meudon, France, carried out computer simulations of the final moments of such an unfortunate star's life，as it veered towards a supermassive black hole.

When the star gets close enough, the uneven forces flatten it into a pancake shape. Some previous studies had suggested this flattening would increase the density and temperature inside the star enough to trigger intense nuclear reactions that would tear it apart. But other studies had suggested that the picture would be complicated by shock waves generated during the flattening process and that no nuclear explosion should occur.

The new simulations investigated the effects of shock waves in detail，and found that even when their effects are included，the conditions favor a nuclear explosion. "There will be an explosion of the star-it will be completely destroyed," Brassart says. Although the explosion obliterates the star, it saves some of the star's matter from being devoured by the black hole. The explosion is powerful enough to hurl much of the star's matter out of the black hole's reach, he says.

The devouring of stars by black holes may already have been observed, although at a much later stage. It is thought that several months after the event that rips the star apart，its matter starts swirling into the hole itself. It heats up as it does so, releasing ultraviolet light and X-rays.

If stars disrupted near black holes really do explode, then they could in principle allow these events to be detected at a much earlier stage, says Jules Hatpern of Columbia University in New York, US. "It may make it possible to see the disruption of that star immediately if it gets hot enough," he says.

Brassart agrees. "Perhaps it can be observed in the X-rays and gamma rays, but it's something that needs to be more studied," he says. Supernova researcher Chris Fryer of the Los Alamos National Laboratory in Los Alamos, New Mexico, US, says the deaths of these stars are difficult to simulate, and he is not sure whether the researchers have proven their case that they explode in the process.

31.【題干】Something destructive could happen to a star that gets too close to a black hole. Which of the following destructive statements is NOT mentioned in the passage?

【選項】

A.The black hole could tear apart the star.

B.The black hole could trigger a nuclear explosion in the star.

C.The black hole could dwindle its size considerably.

D.The black hole could devour the star.

【答案】C

【解析】

32.【題干】According to the third paragraph，researchers differed from each other in the problem of_____

【選項】

A.whether nuclear reaction would occur.

B.whether the stars would increase its density and temperature.

C.whether shock waves would occur.

D.whether the uneven forces would flatten the stars.

【答案】A

【解析】

33.【題干】According to the fourth paragraph，which of the following is NOT true?

【選項】

A.No nuclear explosion would be triggered inside the star.

B.The star would be destroyed completely.

C.Much of the star's matter thrown by the explosion would be beyond the black hole's reach.

D.The black hole would completely devour the star.

【答案】D

【解析】

34.【題干】What will happen several months after the explosion of the star?

【選項】

A.The star's matter will move further away from by the black hole.

B.The black hole's matter will heat up.

C.The torn star's matter will swirl into the black hole.

D.The black hole's matter will release ultraviolet light and X-rays.

【答案】C

【解析】

35.【題干】According to the context，the word "disruption" in Paragraph 6 means_____

【選項】

A."Confusion."

B."Tearing apart."

C."Interruption."

D."Flattening."

【答案】B

【解析】

第二篇 Deforestation and Desertification(沙漠化)

TheSahel zone lies between the Saharadesert and the fertile savannahs(熱帶大草原)ofnorthern Nigeria and South Sudan. The word sahel comes from Arabic and means marginal or transitional ,andthis is a good description of thesesemi-arid(半干旱)lands,whichoccupy much of the Western African countries of Mail,Mauritania,Niger,and Chad.

Unfortunately, over the last century theSahara desert has steadily crept southwards eating into once productive Sahellands. United Nations surveys show that over 70 percent of the dry land inagriculture use in Africa has deterioratedover the last 30 years. Droughts have become more severe, the most recentlasting over twenty years in parts of the Sahel region. The same process ofdesertification is taking place across southern Africa as the Kalahari desertadvances into Botswana and parts of South Africa.

One ofthe major causes of this desert advance ispoor agricultural land use, driven by the pressures of increasing population.Overgrazing一 keeping too many farm animals on the land一means that grasses and other plants cannot recover, and scarce water suppliesare exhausted. Overcultivation一 tryingto grow too many crops on poor land一 resultsin the soil becoming even less fertile and drier, and beginning to break up. Soilerosion (侵蝕) follows, and the land turns into desert.

Another cause of desertification is loss of tree cover. Trees are cutdown for use as fuel and to clear land for agricultural use. Tree roots help tobind the soil together, to conserve moisture, and to provide a habitat forother plants and animals. When trees are cut down, the soil begins to dry andloosen, wind and rain erosion increase, other plant species die, and eventuallythe fertile top soil may be almost entirely lost, leaving only bare rock anddust.

The effects of loss of topsoil and increased drought are irreversible. Theyare,however, preventable. Careful conservation of tree cover and sustainableagricultural land use have been shown to halt deterioration of soils and lessenthe effects of shortage of rainfall. One project in Kita in south-west Malifunded by UNDP has involved local communities in sustainable management offorest,while at the same time providing a viable(有活力的)agriculturaleconomy. This may be a model for similar projects in otherWest African countries.

35 order to prevent desertification,the author proposes ___.

A. making good use of international aids

B. developing a sustainableagricultural economy

C. gaining international support

D. converting agricultural land intoforest

答案：b

36.The Sahel zone is an area which ___.

A. is covered with sad and grass

B. has a long history

C. occupies much of South Nigeria

D. belongs to Sudan

答案：a

37. What is the situation about thedesertification in Africa?

A. The deserts are replaced withgrasslands

B. The deserts are expanding

C. the deserts are moving northwards

D. the deserts are being deserted

答案：b

38. The word “deteriorated ” in paragraph2 means ___.

A. deepened

B. suffered

C. slipped

D. worsened

答案：d

39. What is the root causeof desertification?

A. poor farming

B. overpopulation

C. radical climate change

D. disappearance of rare plant species

答案：a

40. In order to prevent desertification,the author proposes ___.

A. making good use of international aids

B. developing a sustainableagricultural economy

C. gaining international support

D. converting agricultural land intoforest

答案：b

第三篇

OlderVolcanic Eruptions

Volcanoes were more destructive in ancient history, not because theywere bigger，but because the carbon dioxide(二氧化碳)theyreleased wiped out life with greater ease.

Paul Wignall from the University of Leeds was investigating the linkbetween volcanic eruptions and mass extinctions. Not all volcanic eruptionskilled off large numbers of animals, but all the mass extinctions over the past300 million years coincided with huge formations of volcanic rock. To hissurprise, the older the massive volcanic eruptions were, the more damage theyseemed to do. He calculated the "killing efficiency" for thesevolcanoes by comparing the proportion of life they killed off with the volumeof lava (熔巖) that they produced. He found that sizefor size, older eruptions were at least 10 times as effective at wiping outlife as their more recent rivals

The Permian (二疊紀)extinction, for example, which happened 250 million years ago, is marked byfloods of volcanic rock in Siberia that cover an area roughly the size ofwestern Europe. Those volcanoes are thought to have pumped out about 10gigatonnes (十億噸) of carbon as carbon dioxide. The globalwarming that followed wiped out 80 percent of all marine genera (種類)at the time, and it took 5 million years for the planet to recover. Yet 60million years ago, there was another huge amount of volcanic activity andglobal warming but no mass extindtion. Some animals did disappear but thingsreturned to normal within tens of thousands of years. "The most recentones hardly have an effect at all," Wignall says. He ignored theextinction which wiped out the dinosaurs (恐龍) 65million years ago, because many scientists believe it was primarily caused bythe impact of an asteroid (小行星). Hethinks that older volcanoes had more killing power because more recent lifeforms were better adapted to dealing with increased levels of CO2.

Vincent Courtillot, director of the Paris Geophysical Institute in France,says that Wignall's idea is provocative. But he says it is incredibly hard todo these sorts of calculations. He points out that the killing power ofvolcanic eruptions depends on how long they lasted. And it is impossible totell whether the huge blasts lasted for thousands

or millions of years. He also adds that itis difficult to estimate how much lava prehistoric volcanoes produced, and thatlava volume may not necessarily correspond to carbon dioxide emissions.

41.Older volcanic eruptions did moredamage than more recent ones because

A. older volcanoes were brighter.

B. carbon dioxide made the earth muchwarmer

C. older volcanoes were hotter

D. carbon dioxide killed off life moreeasily

答案：d

42. Wignall calculated the killing powerof those older volcanic eruptions by

A. estimating how long they lasted

B. counting the dinosaurs they killed

C. comparing the proportion of lifekilled with the volume of lava produced

D. studying the chemical composition oflava

答案：c

43. When did dinosaurs become extinct?

A. 300 million years ago.

B. 250 million years ago

C. 65 million years ago

D. 60 million years ago

答案：c

44. It can be inferred from Paragraph 3that the cause of dinosaur extinction is_______

A. a political issue.

B. self-evident.

C. quite certain

D. controversial

答案：d

45. What is the main thesis of thearticle?

A. Volcanic eruptions are not alwaysdeadly.

B. Carbon dioxide emissions often giverise to global warming.

C. Older volcanic eruptions are moredestructive

D. It is not easy to calculate the killingpower of a volcanic eruption

答案：c

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