The correct answer is The Mississippi. Explanation & Key Takeaways: • The Mississippi River is the longest river in the United States. • It has a total length of approximately 2,340 miles. • The river flows through 10 states: Minnesota, Wisconsin, Iowa, Illinois, Missouri, Kentucky, Tennessee, Arkansas, Mississippi, and Louisiana. • It is a vital waterway for transportation, agriculture, and commerce in the United States. Related Concepts: • The Missouri River, which is a tributary of the Mississippi River, is slightly longer but is considered a separate river system. • The Mississippi River plays a crucial role in the ecosystem, providing habitats for numerous species of fish, birds, and other wildlife. • It is known for its historical significance, as it has been central to exploration, trade, and cultural development in the United States.