練習：

　　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 Saturns 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"this form 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.

　　答案與題解：

　　1. C 短文的第一段提供了答案。該段告訴讀者，科學家在土星的衛星土衛六( Titan )上發現了生命的跡象，這些生命的存在是以甲烷為基礎的。

　　2.A根據第二段"Scientists have reportedly discovered clues showing primitive alien beings are "breathing" in Titans dense atmosphere filled with hydrogen."，說明土衛六(Titan)有生命跡象。因此A是答案。

　　3. B this form of life 指的是土衛六( Titan )上以甲烷為生命基礎呼吸氫氣的生物，即該文討論的主題。

　　4.A科學家至今對土衛六是否存在生物有不同的觀點和解釋。Allen 說要做出土衛六上有生

　　物的結論，首先必須對Titan 上沒有生物的觀點做出回應；要排除土衛六上可能沒有生物的觀點，我們還須付出努力。所以只有A是正確選擇。

　　5.D該短文的主題是，科學家在土衛六( Titan )上發現了一種與地球生物不同的生命形式的跡象，即以甲烷為生命基礎呼吸氫氣的生物，但科學家還未能最后驗證這一發現。第四段中的一個句子能夠揭示該短文的主題："If these signs do turn out to be a sign of life， it would bedoubly exciting because it would represent a second form of life independent from water-based life on Earth."