单项选择题

Wht does theuthor men by sying tht the Grnd Cnyon is of reltively recent origin Wht does t

heuthor men by sying tht the Grnd Cnyon is of reltively recent origin The riverlmost completed its work of erosion onlybout six million yersgo. B．The Colordo Plteu only rose comprtively short time from now. C．Volcnic debrisnd intrusions of igneous rockre of recent origin. D．The form. of the cnyon is the result of the recent work done by the nturl force.A．The river almost completed its work of erosion only about six million years ago．B．The Colorado Plateau only rose a comparatively short time from now．C．Volcanic debris and intrusions of igneous rock are of recent origin．D．The form． of the canyon is the result of the recent work done by the natural forcE．

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Wht ________ if there ______ no wter orir on the erth hppen, isB．will hppen, isC．will hppe

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Both in what is now the eastern and the southwestern United States, the peoples of the ArBoth in what is now the eastern and the southwestern United States, the peoples of the Archaic era （）

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