ns. Not all volcanic eruptionskilled offlarge numbers of animals, but all the mass extinctions over the past300 millionyears coincided with huge formations of volcanic rock. To hissurprise, the olderthe massive volcanic eruptions were, the more damage theyseemed to do. Hecalculated the "killing efficiency" for thesevolcanoes by comparing theproportion of life they killed off with the volumeof lava (熔岩) that theyproduced. He found that sizefor size, older eruptions were at least 10 times aseffective at wiping outlife as their more recent rivals
The Permian (二叠纪)extinction, for example, which happened 250 million yearsago, is marked byfloods of volcanic rock in Siberia that cover an area roughlythe size ofwestern Europe. Those volcanoes are thought to have pumped out about10gigatonnes (十亿吨) of carbon as carbon dioxide. The globalwarming that followedwiped out 80 percent of all marine genera (种类)at the time, and it took 5 millionyears for the planet to recover. Yet 60million years ago, there was another hugeamount of volcanic activity andglobal warming but no mass extindtion. Someanimals did disappear but thingsreturned to normal within tens of thousands ofyears. "The most recentones hardly have an effect at all," Wignall says. Heignored theextinction which wiped out the dinosaurs (恐龙) 65million years ago,because many scientists believe it was primarily caused bythe impact of anasteroid (小行星). Hethinks that older volcanoes had more killing power becausemore recent lifeforms were better adapted to dealing with increased levels ofCO2.
Vincent Courtillot, director of the Paris Geophysical Institute inFrance,says that Wignall's idea is provocative. But he says it is incrediblyhard todo these sorts of calculations. He points out that the killing powerofvolcanic eruptions depends on how long they lasted. And it is impossibletotell whether the huge blasts lasted for thousands
or millions of years. He also adds that itis difficult to estimate how muchlava prehistoric volcanoes produced, and thatlava volume may not necessarilycorrespond 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 eruptionsby
A. estimating how long they lasted
B. counting the dinosaurs they killed
C. comparing the proportion of lifekilled with the volume of lavaproduced
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 extinctionis_______
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
完形填空
CellPhone Lets Your Secrets Out
Your cell phone holds secrets about you.Besides the names and numbers thatyou've programmed into it, ______traces____(51) of your DNA linger (遗留) onthedevice according to a new study
DNA is genetic (遗传的)material _____that_____ (52) appears in every cell. Likeyour fingerprint, yourDNA is _____unique______ (53) to you——unless you have anidentical twin. Scientiststoday analyze DNA in blood, saliva (唾液), orhair left____behind_______ (54) at the scene of a crime. The results oftenhelp detectivesidentify ____criminals______ (55) and their victims. Your cellphone can revealmore about you ____than_____ (56) you might think.
Meghan J. McFadden, a scientist at McMasterUniversity in Hamilton, Ontario,heard about a crime in which the suspect bledonto a cell phone and later droppedthe____device_____ (57). This made herwonder whether traces of DNA lingered oncell phones一evenwhen no blood was___involved_____(58). She and colleagueMargaret Wallace ofthe City University of NewYork analyzed the flip-openphones(翻盖手机)of10 volunteers. They used swabs (药签) tocollect _____invisible___(59) traces of the users from two parts of the phone:the outside, where the user____holds_____(60) it, and the speaker which isplaced at the user's ear
The scientists cleaned the phones using asolution made mostly__of____(61)alcohol. The aim of washing was to remove alldetectable traces of DNA. Theowners got their phones back for another week.Then the researchers___returned________ (62) the phones and cleaned each phoneonce more.
The scientists discovered DNA that _____belonged______(63) to the phone'sspeaker on each of the phones. Better samples werecollected from the outside ofeach phone, but those swabs also picked up DNAthat belonged to other people whohad apparently also ____handed______ (64) thephone
Surprisingly, DNA showed up even in swabsthat were taken immediately afterthe phones were scrubbed. That suggests thatwashing won't remove all traces of___evidence________ (65) from a criminal'sdevice. So cell phones can now beadded to the list of clues that can clinch (确定)a crime-scene investigation.
51. A. name B.pictures C. shapes D. traces
答案：d
52. A. that B. while C.as D.what
答案：a
53. A. common B. good C. helpful D. unique
答案：d
54. A. behind B. away C. aside D.over
答案：a
55. A. visitors B. travelers C.scientists D.criminals
答案：d
56. A. until B. before C.unless D. than
答案：d
57. A. paper B. document
C. device D.file
答案：c
58. A. checked B. involved C. tested D. gathered
答案：b
59. A. invisible B.emotional C. poiso
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