Now listen to the four statements. Statement (D) best describes what you see in the picture. Therefore, you should choose answer (D). A. He is on the phone B. She is driving the car C. She is typing on the computer D. He is sitting next to her

Canyon formation fundamentally requires uplift. This can mean either vertical movement of rock with respect to a fixed reference frame (e.g. sea level) or a drop in the base level to which the river drains. The materials that the river flows over can play a role, with generally more competent (i.e. resistant to erosion) rocks promoting canyon development as steeper walls can be maintained, but without uplift, a canyon will not form. Comparing the Colorado and the Mississippi, the fundamental difference is that the Colorado Plateau, through which the Grand Canyon has incised, has experienced significant uplilft, where as the center of the North American continent is not experiencing significant uplift.

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