NASA scientists searching for clues of “ancient water” on Mars now feel they have photographic evidence of recent water flow in some of the gullies （冲沟）that lace the planet’s surface.

    The changing appearance of gullies on Mars over the last seven years suggests that liquid water flowed recently on the Red Planet and may still seep out in brief bursts, researchers said Wednesday.

    New images of known gullies on Mars show evidence of new flows and deposits, pointing to explosive events in which some form of water burst from crater（弹坑） walls and ran down their slopes and support what researchers call “the squirting gun” theory.

    “We’ve had this story of ancient water on Mars,” researcher Kenneth Edgett, who participated in the Mars gully study, said during a news briefing at NASA’s Washington headquarters. “Today we’re talking about liquid water that is present on Mars right now.”

    Edgett and colleagues utilized images from NASA’s Mars Global Survivor to study regions earlier this year where gullies, depressionlike landforms on the Red Planet’s surface, were found in 2000.

    They found new, light-colored deposits that do not appear to have formed from landslides, but could be the work of frost, salt deposits or long-sought evidence that water flowed recently on Mars. The research is detailed in this week’s issue of the journal Science.

    Christensen said the questions still to be answered include determining the source of water at the gully sites, and making in-depth spectral analyses to confirm the photographic evidence of liquid water.

    Pinning down the source of any liquid water source, be it a subsurface aquifer（水土层）, ice pack or melting snow, is key, he added.

    “The great news is that NASA has the tools to do that,” said Christensen, who also serves as the principal investigator for the Thermal Emission Imaging System aboard NASA’s 2001 Mars Odyssey orbiter, currently circling Mars. “I think we’re really positioned to go forward with a view of Mars as a dynamic, active place.”

    New light-toned deposits coating gullies in April 2005 that were not present in December 2001 were found in an area known as Terra Sirenum. Similar differences were seen in a crater etched into the Centauri Montes region of Mars, which apparently changed sometime between August 1999 and February 2004.

    “I think this is pretty interesting evidence that says yes, there is subsurface water,” Christensen said, adding that aquifers, snow packs and ground ice are all plausible（似是而非）sources for liquid Martian water. “It remains to see which ones are most plausible.”

    1. What evidence supports what researchers call “the squirting gun” theory? ________________
    A. The changing appearance of gullies.
    B. Explosive events.
    C. Some form of water that burst from the crater walls and ran down their slpoes.
    D. Liquid water flowed recently on the Red Planet.
    2. According to Christensen, _______ is the most important to confirm the photographic evidence of liquid water on Mars?
    A. finding out the source of any liquid water source
    B. making a in-depth spectral analysis
    C. finding a subsurface aquifer, ice pack or melting snow
    D. finding a lot of water
    3. The following are plausible resources for liquid Martian water except ________________ .
    A. aquifer          B. snow pack
    C. ground ice       D. subsurface water
    4. According to the report, ______________.
    A. The source of liquid water on Mars has been found
    B. The changing appearance of gullies suggests that there is liquid water flowing on the surface of Mars
    C. Aquifers are the most plausible source of liquid water
    D. Aquifers, snow packs and ground ice are all plausible （似是而非）sources for liquid Martian water

    Keys：1. C  2. A  3. D  4. D
    解析： 1. 从第三段中“ . . . pointing to explosive events in which some form of water burst from crater（弹坑） walls and ran down their slopes and support what researchers call ”the squirting gun“ theory.”可以得到答案。
    2. 由“Pinning down the source of any liquid water source . . . is key  . . . ”可以得到正确答案。“Pin down”意思是“确定，弄清楚”。
    3. D答案是一个笼统的东西，A、B、C三项都属于地下水.

    4. 从文中最后一段可以直接得到答案。

    小结：细节性问题是关于SUPPORTING DETAILS 类的问题，通过SKIMMING找出主题后，应进一步掌握阐述和发展主题的主要事实，或按要求找出特定细节。在回答此类问题时，应采用查读法（SCANNING）,因为这些具体内容（details）是用来说明、论证或分析文章中心的。这类题目常以“wh-”形式来提问，如who, what, when, why及how等形式。这些问题的表达不采用文章中的原话提问，而是使用同义词语等，因此，在选择答案前应首先看清题干，然后在查读时寻找与题目相关的关键词语；最后，在充分理解原文、原题的基础上选定正确的答案。

    当然，这类细节性问题涉及的面很广。有的涉及数字计算，如时间、距离、次数、数量等，对这类问题须认真计算后方可选定正确答案；有的涉及正误判断，要先看选项，根据选项提供的线索，寻找文中相应部分，最后在题中选出肯定答案；还有的是有关事实、原因、结果、目的等。总之，做细节题切忌通过自己对某类知识的主观了解和认识做出轻率判断，一定要紧扣文章内容，不可随心所欲。

    细节类问题的命题方式有以下几种：

    （1）Which of the following is NOT true according to the information in the passage?
    （2）Which of the following is mentioned in the passage?
    （3）What is the example of . . . as described in the passage?
    （4）The author mentions all of the following except . . .
    （5）The reason for . . . is . . .
    （6）The author states that . . .
    （7）According to the passage, when （where, why, how, who, etc） . . . 

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