In 1994, a team of scientists led by David Mckay began studying the meteorite ALH84001, which had been Line discovered in Antarctica in 1984. (5) Two years later, the McKay team announced that ALH84001, which scientists generally agree originated on Mars, contained compelling evi- dence that life once existed on Mars. (10) This evidence includes the discovery of organic molecules in ALH84001, the first ever found in Martian rock. Organic molecules—complex, carbon- based compounds—form the basis for (15) terrestrial life. The organic molecules found in ALH84001 are polycyclic aro- matic hydrocarbons, or PAH’s. When microbes die, their organic material often decays into PAH’s. (20) Skepticism about the McKay team’s claim remains, however. For example, ALH84001 has been on earth for 13,000 years, suggesting to some scientists that its PAH’s might have (25) resulted form terrestrial contamination. However, McKay’s team has demon- strated that the concentration of PAH’s increases as one looks deeper into ALH84001, contrary to what one would (30) expect from terrestrial contamination. The skeptic’s strongest argument, however, is that processes unrelated to organic life can easily produce all the evidence found by McKay’ steam, (35) including PAH’s. For example, star formation produces PAH’s. Moreover, PAH’s frequently appear in other meteorites, and no one attributes their presence to life processes. (40) Yet McKay’s team notes that the particular combination of PAH’s in ALH84001 is more similar to the combinations produced by decaying organisms than to those originating form nonbiological processes. The primary purpose of the passage is to - describe new ways of studying the possibility that life once existed on Mars
- revise a theory regarding the existence of life on Mars in light of new evidence
- reconcile conflicting viewpoints regarding the possibility that life once existed on Mars
- evaluate a recently proposed argument concerning the origin of ALH84001
- describe a controversy concerning the significance of evidence from ALH84001
答案是E,但是文中一直讨论得是火星上得证据究竟是不是能证明它上面有生命存在,哪里体现了concerning the significance of evidence from ALH84001?? BTW,C是不是错在文章只有2个观点,一个支持火星有生命,一个反对,无众多观点,对不对? |