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  3. Perched among the highlands of western Cameroon, bordered by green mountains and cliff faces, Lake Nyos is a scene of breathtaki

Perched among the highlands of western Cameroon, bordered by green mountains and cliff faces, Lake Nyos is a scene of breathtaki

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问题     Perched among the highlands of western Cameroon, bordered by green mountains and cliff faces, Lake Nyos is a scene of breathtaking beauty. But the picture cannot be【B1】______.A detailed study reveals that the lake could release a【B2】______cloud of car bon dioxide, capable of wiping out entire communities around its shores.
    The warning, from a team of scientists, comes nearly 20 years after the lake【B3】______an estimated 80m cubic metres of CO2 into the atmosphere. Heavier than air, the cloud of gas rolled down,【B4】______hillsides and villages. Silent and invisible, it【B5】______the air of oxygen, killing hundreds of cattle and claiming the lives of more than 1,700 people up to 26km away. "It was one of the most mysterious【B6】______scientists have ever investigated" said George Kling, an ecologist at the University of Michigan.
    Researchers called in after the 1986【B7】______discovered that the lake, which sits atop a volcano, contained record levels of carbon dioxide.  Gas bubbling up from the Earth’s magma was under such【B8】______at the bottom of the 200-metres deep lake that it dissolved until it reached max.【B9】______.
    To prevent a recurrence, in 2001 engineers installed a pipe to suck CO2 from the bottom of the lake and release it harmlessly into the air.【B10】______. Dr Kling’s team recommends the urgent installation of a further four pipes in each lake at a rate of one a year.【B11】______.
【B5】
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答案exhausted
解析 此题考查听特定信息的能力。解题的关键在于抓住上句所用的时态为一般过去时，由于此句还是在描述湖水释放二氧化碳的情景，所以要用过去时。
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