[单项选择]

Grand Canyon

How was the Grand Canyon formed The truth is that no one knows for sure though there are some pretty good guesses, and it is usually thought that a number of processes combined to create the views that you see in today’s Grand Canyon. The most powerful force to have an impact on the Grand Canyon is erosion, primarily by water (and ice) and secondly by wind. Other forces that contributed to the Canyon’s formation are the course of the Colorado River itself, vulcanism, continental drift and slight variations in the earth’s orbit which in turn causes variations in seasons and climate.
Water seems to have had the most impact basically because our planet has lots of it and it is always on the move. Many people cannot understand how water can have such a profound impact considering that the Canyon is basically located in a desert. This is one of the biggest reasons that water has such a big impact here. Because the soil
A. the weather there is bad
B. the canyon is too long
C. the flood there is dangerous
D. there are many storms