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  3. Yellowstone National Park is the oldest national park in the world. About three million people visit it each year. Its great nat

Yellowstone National Park is the oldest national park in the world. About three million people visit it each year. Its great nat

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问题     Yellowstone National Park is the oldest national park in the world. About three million people visit it each year. Its great natural beauty has made it one of the most popular national parks.
    Most visitors like to see "Old Faithful," the world’s most famous geyser. A geyser shoots hot water high into the air. There are more than three hundred geysers in Yellowstone.
    Old Faithful is not the biggest or the most beautiful geyser. But it is the most popular. Visitors gather around Old Faithful before each eruption. Experts at the park are able to predict when these will happen. The average time between eruptions is about ninety minutes. Old Faithful shoots water an average of forty meters into the air. This eruption lasts between two and five minutes. Old Faithful releases up to about thirty thousand liters of water into the air each time.
    The hot spot deep under the ground produces geysers like Old Faithful. Old Faithful is evidence of the volcanic activity at Yellowstone. But will the Yellowstone volcano erupt again? Most experts think the answer is yes. But no one knows when. The most recent of the three extremely powerful eruptions was about six hundred fifty thousand years ago.
    Experts say at least thirty smaller volcanic eruptions have taken place at Yellowstone. Some of these were perhaps as big as the nineteen ninety-one eruption at Mount Pinatubo in the Philippines. Several are believed to have been much larger. The most recent of these smaller eruptions took place about seventy thousand years ago.
    Volcano experts say it is extremely difficult to tell when Yellowstone might become an active volcano again. However, earthquakes near a volcano are usually good evidence that a volcano might become active again. For example, Mount Saint Helens in the northwestern state of Washington exploded in nineteen eighty. Several earthquakes took place near the volcano before that time. On the morning that it exploded, Mount Saint Helens experienced an earthquake of five point one on the Richter scale.
    Yellowstone National Park experiences several thousand earthquakes each year. Most are very small. They cannot be felt. They can only be measured by scientific instruments. However, in August of nineteen fifty-nine, an earthquake at Yellowstone measured seven point five on the Richter scale. Twenty-eight people were killed.
    It was one of the strongest earthquakes ever recorded in the United States. But Yellowstone’s sleeping giant volcano did not erupt.
    In two thousand one, the United States Geological Survey, Yellowstone National Park and the University of Utah signed an agreement.
    That agreement established the Yellowstone Volcano Observatory. Under the agreement, the park, the Geological Survey and the university are responsible for improving efforts to study the volcanic system of Yellowstone.
    The observatory uses information from many different instruments on the ground and from satellites to study the volcano. The information will help officials decide if Yellowstone’s huge volcano is becoming a danger. Then they could warn the public quickly if necessary.
    Experts at the observatory say Yellowstone represents some danger to the public. It always has. However, its natural beauty also makes it a treasure that could not be possible without the sleeping giant volcano that is under Yellowstone National Park.
Experts at the observatory are most concerned about
选项 A、when the next earthquake happens.
B、when the volcano becomes active.
C、if the volcano threatens the public.
D、if the volcano will erupt before long.
答案D
解析 根据题干中的experts和observatory定位到最后三段。第3段第3句和倒数第2段最后两句表明专家担忧的是黄石国家公园的火山什么时候会再爆发，故应选D。换个角度想，本题的干扰项应该是专家们已经知道的事，根据第4段可推断专家们已知黄石国家公园是一座巨大的活火山，因此B不能选；最后一段开头两句表明C也是无需再作解答的问题。
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