四级阅读专项训练题附答案解析
四级阅读专项训练题原文
"We suggested hydrogen consumption because it’s the obvious gas for life to consumeon Titan,similar to the way we consume oxygen on Earth,"says NASA scientist Chris McKay."Ifthese signs do turn out to be a sign of life,it would be doubly exciting because it wouldrepresent 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 wasteproduct. On Titan, where temperatures are around 90 Kelvin(minus 290 degrees Farenheit),amethanebased organism would have to use a substance that is liquid as its medium forliving processes, but not water itself. Water is frozen solid on Titan’s surface and much too coldto support life as we know it.
Scientists had expected the Sun’s interactions with chemicals in the atmosphere toproduce a coating of acetylene on Titan’s surface. But Cassini detected no acetylene on thesurface.
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 choiceafter all non-biological explanations are addressed,"Allen said. "We have a lot of work to do torule out possible non-biological explanations. It is more likely that a chemical process,withoutbiology,can explain these results."
四级阅读专项训练题
1 .What have scientists found about Saturn?
A They have found a new moon orbiting Saturn.
B They have found methane-based life on Saturn.
C They have found methane-based life on Titan.
D They have found earthlike life on a Saturn’s moon.
2. What do scientists say about Titan?
A There are life clues there.
B There is acetylene there.
C Water on Titan exists in the form of ice.
D Rivers and lakes there contain life formls.
3. To date,scientists have not yet detected this form of life.(paragraph 5)What does"thisform
of life" refer to?
A Water-based life.
B Methane-based life.
C Liquid-water-based microorganisms.
D Gas-based life.
4. What can be inferred from what Allen said?
A Scientists have different arguments over whether there is life on Titan.
B Scientists all agree that there is life on Titan.
C Scientists all suggest that a biological explanation is reasonable.
D Scientists all agree that a non-biological chemical reaction is a possible explanation.
5. Which of the following can replace the title of this passage?
A Earthlike Living Beings Found on Titan.
B Finding of One More Moon of Saturn.
C Titan,a New Satellite Found.
D A different Life Form, a Possibility.
四级阅读专项训练题答案
1. C 短文的第一段提供了答案。该段告诉读者，科学家在土星的卫星土卫六( Titan )上发现了生命的迹象，这些生命的存在是以甲烷为基础的。
2.A根据第二段“Scientists have reportedly discovered clues showing primitive alien beingsare
breathing’ in Titan’s dense atmosphere filled with hydrogen.”，说明土卫六(Titan)有生命迹象。因此A是答案。
3. B this form of life 指的是土卫六( Titan )上以甲烷为生命基础呼吸氢气的生物，即该文讨论的主题。
4.A科学家至今对土卫六是否存在生物有不同的观点和解释。Allen 说要做出土卫六上有生
物的结论，首先必须对Titan 上没有生物的观点做出回应;要排除土卫六上可能没有生物的观点，我们还须付出努力。所以只有A是正确选择。
5.D该短文的主题是，科学家在土卫六(Titan)上发现了一种与地球生物不同的生命形式的迹象，即以甲烷为生命基础呼吸氢气的生物，但科学家还未能最后验证这一发现。第四段中的一个句子能够揭示该短文的主题：“If these signs do turn out to be a sign of life, it would bedoubly exciting because it wouldrepresent a second form of life independent from water-based life on Earth.”