Read these sentences from the text. "Whoever they became, and however Cahokia fell, another important archaeological mystery yet remains. Possible descendants include the peoples of great American Indian Nations and tribal groups met by Lewis and Clark in 1804 or painted by George Catlin in the 1830s. Any yet among them, including the Quapaw, Omaha, Pawnee, and others, there are no stories that speak of the city of Cahokia. Why might the descendants of Cahokia have chosen to forget Cahokia? The answers might remain in the ruins of Cahokia, the central portion of which is preserved within Illinois' Cahokia Mounds State Historic Site." What might be the author's purpose for asking the question, "Why might the descendants of Cahokia have chosen to forget Cahokia?"