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In North America, the continental divide runs through the Rocky Mountains of the United States and the Sierra Madre of Mexico. It is an imaginary line that scientists use to mark something. The continental divide in North America marks the point where rivers change their flow. On the west side of the divide, rivers flow west into the Pacific Ocean. On the east side, rivers flow east, eventually emptying into the Atlantic Ocean. South America, Africa, Asia and Europe each have a continental divide, as well.
This selection mainly describes
A. why continents have rivers
B. how rivers flow
C. what a continental divide is
D. how scientist understand the continents
What is C.