题目内容：
第4题___________
A．Three calderas make up more than a third of Yellowstone National Park. B．The first Yellowstone eruption,2 million years ago, released more than double that amount of ash and debris.
C．The volcano is so inconspicuous (不显眼的 ) that few people know it exists.
D．Then, an enormous fountain will shoot high into the air.
E．While the active geological processes at Yellowstone do pose some risk to the public, they also make it a unique treasure.
F．Yellowstone National Park attracts the interest of geologists the world over.
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