Question

The beaver has four gnawing incisors, two uppers and two lowers, that are rather ingeniously adapted to woodcutting. They grow constantly and wear with use to a chisel edge. The back side of the tooth, because it is made of a soft dentine, wears down, whereas the front side, outer-layered as it is with a very strong orange-colored enamel, doesn't. The beaver has lips that can close behind the incisors to keep the mouth free of wood chips and, when the beaver is gnawing underwater, water. The beaver is the largest rodent in North America.

Answer 1

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Answer 2

@sengland