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"Life Form Found" on Saturn's Titan

Scientists say they have discovered hints of alien life on the Saturn's moon.The discovery of a sort of life was announced after researchers at the US space agency,NASA,analyzed data from spacecraft Cassini,which pointed to the existence of methane-based form of life on Saturn's biggest moon.

Scientists have reportedly discovered clues showing primitive alien beings are"breathing" in Titan's dense atmosphere filled with hydrogen.

They argue that hydrogen gets absorbed before hitting Titan's planet-like surface covered with methane lakes and rivers.This,they say,points to the existence of some"bugs" consuming the hydrogen at the surface of the moon less than half the size of the Earth.

"We suggested hydrogen consumption because it's the obvious gas for life to consume on Titan,similar to the way we consume oxygen on Earth,"says NASA scientist Chris McKay."If these signs do turn out to be a sign of life,it would be doubly exciting because it would represent a second form of life independent from water-based life on Earth."To date,scientists have not yet detected this form of life anywhere,though there are liquid-water-based microorganisms on Earth that grow well on methane or produce it as a waste product.On Titan,where temperatures are around 90 Kelvin （minus 290 degrees Farenheit）,a methanebased organism would have to use a substance that is liquid as its medium for living processes,but not water itself.Water is frozen solid on Titan's surface and much too cold to support life as we know it.

Scientists had expected the Sun's interactions with chemicals in the atmosphere to produce a coating of acetylene on Titan's surface.But Cassini detected no acetylene on the surface.

The absence of detectable acetylene on the Titan's surface can very well have a non-biological explanation,said Mark Allen,a principal investigator of the NASA Titan team.

"Scientific conservatism suggests that a biological explanation should be the last choice after all non-biological explanations are addressed,"Allen said."We have a lot of work to do to rule out possible non-biological explanations.It is more likely that a chemical process,without biology,can explain these results."

41 .What do scientists claim to have found about Saturn？

A.Water-based life on it.

B.Methane-based life on its biggest moon.

C.A new moon moving around it.

D.Earthlike life on its biggest moon.

[参考答案]B

[解析]题意：科学家声称在土星上发现了什么？

根据文章第一段Scientists say they have discovered hints of alien life on the Saturn‘s moon…the existence of methane—based form of life on Saturn’s biggest moon可知,科学家声称在土星最大的卫星 上发现了存在甲烷为基础的生命形式。故选B.

42.Which of the following statements about Titan is true？

A.It is as large as the Earth.

B.There is acetylene on its surface.

C.Water on it acts as a life supporting medium.

D.Hydrogen consumption is reported to be on it.

[参考答案]D

[解析]题意：下列关于土卫六的说法哪个是正确的？

根据文章第二段Scientists have reportedly discovered clues showing primitive alien beings are “breathing”in Titan‘s dense atmosphere filled with hydrogen可知,科学家们报导他们发现了被氢气环 绕的土卫六上有原始外星生物“呼吸”的线索,由第三段第二句…they say,points to the existence of some“bugs”consuming the hydrogen at the surface of the moon less than half the size of the Earth.进一步得知这种外星生物是消耗氢气的,故D项正确。由第三段第二句也可知土卫六的大小不到地球的一半,由此A项错误。由第六段Scientists had expected…a coating of acetylene on Titan’s surface.But Cassini detected no acetylene on the surface可知,太空船并没有探测到土卫六表面有乙炔的存在,故B项错误。根据第五段第二、三句on Titan…a methane—based organism would have to use a sub— stance that is liquid as its medium for living processes,but not water itself.Water…much too cold to support lire可知以甲烷为基础的生物可以利用液体作为生命活动的介质,但却不是水,故C项错误。所以本题选D.

43.The expression "this form of life" in paragraph 5 refer to？

A.Water-based life.

B.oxygen-based life.

C.Methane-based life.

D.Liquid-based microorganisms.

[参考答案]C

[解析]题意：第五段中“this form of life”指的是什么？

根据第四段第一句…similar to the way we consume oxygen on Earth可知耗氧生物体存在于地球上,故B项错误。本段最后一句…it would represent a second form of life independent from water— based lire on Earth说明这种生命形式与地球上以水为介质的生物不同,故A项错误。根据第五段 though there are liquid—water—based microorganisms on Earth…a methane—based organism would have to use a substance that is liquid as its medium for living processes可知这种生命形式的确是以液体为介质进行生命活动的,但并没有明它们是微生物,故C项错误,同时根据本句和第一段最后一句…the existence of methane—based form of life得知这种生物是基于甲烷的,故C项正确。故选C.

44.It can be inferred from Mark Allen‘s address that

A.Scientists are trying to confirm these is life on Titan.

B.Scientists agree that a chemical process is a convincing explanation.

C.Scientists share the opinion that a biological explanation is reasonable.

D.Scientists are arguing over whether there is life on Titan.

[参考答案]A

[解析]题意：通过马克？艾伦的话可以得出什么结论？

根据文中最后一段倒数第一、二句艾伦所说We have a lot of work to do to rule out possible non— biological explanations.It is more likely that a chemical process,without biology,can explain these results可知,科学家们希望通过排除法来确定土卫六上生物体的存在,因为他们发现的这些结果也可能以化学反应来解释。故A项正确,而B项“科学家们认为化学反应是令人信服的解释”,C项“科学家们都认为生物学的解释是合理的”都错误。D项具有一定的迷惑性,由最后一段可得知科学家们在为他们所得的数据找出合理的解释,而并不是在争论到底土卫六上有没有生物,故D项错误。所以本题选A.

45.Which of the following can replace the title of this passage？

A .A different Life Form,a Possibility.

B.Earthlike Living Beings Found on Titan.

C.Finding of One More Moon of Saturn‘s.

D.Titan,a New Satellite Discovered.

[参考答案]A

[解析]题意：下列哪个能取代原标题作为本文的标题？

文章标题是《土卫六上发现的生命形式》,能替代的只有A选项：《其他生命形式的存在是有可能的》。B项Earthlike Living Beings Found on Titan,由文章第四、五段可知这种生物形式与地球上的生物是不同的,故B项错误。文章通篇都在谈论关于土卫六上的可能存在的生物,对于C项和D项没有涉及,故C项和D项错误。所以本题选A.