Task: Question Generation
Input (English): Tennessee (i/tɛnᵻˈsiː/) (Cherokee: ᏔᎾᏏ, Tanasi) is a state located in the southeastern United States. Tennessee is the 36th largest and the 17th most populous of the 50 United States. Tennessee is bordered by Kentucky and Virginia to the north, North Carolina to the east, Georgia, Alabama, and Mississippi to the south, and Arkansas and Missouri to the west. The Appalachian Mountains dominate the eastern part of the state, and the Mississippi River forms the state's western border. Tennessee's capital and second largest city is Nashville, which has a population of 601,222. Memphis is the state's largest city, with a population of 653,450.
Output (English): Which river marks Tennessee's border to the west?