What is the purpose of the statement, "Whereas in 1810 only a seventh of the American people lived west of the Appalachian Mountains, by 1840 more than a third lived there"? A. To illustrate that generally population shifts occur rapidly B. To correct a mistaken impression of American agriculture from 1810 to 1840 C. To emphasize the range and speed with which the westward migration occurred D. To demonstrated how attractive the Appalachian Mountains were to Americans