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  3. 共用题干 第三篇“Life Form Found" on Saturn ' s TitanScientists say they have disc...

共用题干 第三篇“Life Form Found" on Saturn ' s TitanScientists say they have disc...

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问题 共用题干
第三篇

“Life Form Found" on Saturn ' s Titan

Scientists say they have discovered hints of alien life on the Saturn'5 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 minus 17 Kelvin(minus 290 degrees Farenheit),a methane-based 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'5 surface and much too cold to support life as we know it.
Scientists had expected the Sun'5 interactions with chemicals in the atmosphere to produce a coating of
acetylene on Titan'5 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 explana-
tion,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-bio-
logical explanations.It is more likely that a chemical process,without biology,can explain these results."
选项 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
答案C
解析由文章第一段第二句话中“The discovery of...which pointed to the existence of methane- based form of life on Saturn' s biggest moon.”可知，科学家们的证据显示，土星的这个最大的卫 星上有甲烷基的生命形态存在，故选B。
由文章第二、三段的内容可知，科学家们发现有线索显示“土卫六”上原始的外星生物 在由氢气环绕的稠密大气层中“呼吸”，也就是说这个卫星上有氢气的消耗现象。故选D。
由文章前五段的内容可知，科学家在文章开头提出“土卫六”上可能有甲烷基的生命形 态，即methane-based life，接下来的内容给出了科学家们对此说法的一系列证据来进行论证，故 选C。
由文章的最后两段中Mark Allen的话，尤其是文章最后一句“It is more likely that a chemical process ,without biology , can explain these results.”可知，科学家们认为应该用化学过程 来解释为什么“土卫六”表面没有乙炔，故选B。
由文章内容可知，科学家们提出了土星的这个最大的行星上可能有一种不依赖于水的 生命形态，并从各方面进行了证明，故选A。第5部分：补全短文
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