Why does Twain compare memorizing every geographical detail of New York City’s longest street with memorizing every geographical detail of the Mississippi River? A. to show that cities are much more dangerous than natural environments B. to show that unlike city streets, the path of the river never changes C. to make a distinction between a river pilot and even the most knowledgeable pedestrian D. to make the distinction that it’s more difficult to navigate a major city’s street than a long river