The United States has an area of 9.63 million square kilometers, has a population of about 313 million people, have a large number 3 or 4 world. , and has the most population ranked 3 of the world. As a country which has various differences in race and culture.The geography and weather conditions of the United States also have variety extremes. And it is also the home of wild animals vary greatly. The U.S. economy is the national economy, the largest in the world.