When Was Hoover Dam Built?
When Was Hoover Dam Built? Once known as Boulder Dam, Hoover Dam is a concrete arch-gravity dam across the Black Canyon of the Colorado River between the states of...
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What Is Soil?
Soil is a mixture of very small pieces of rock and rotted materials from plants and animals. This rotting plant and animal material, called humus, gives soil its dark...
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How Is Cartilage Different than Bone?
How Is Cartilage Different than Bone? Your nose and your ears allow you to sense things, but there’s something else inside them that they share. The stuff under...
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