Which of the following is the longest river in the world?

Measuring from the headwaters of the most distant source, the five longest rivers in the world are the Nile (in eastern and northeastern Africa), the Amazon–Ucayali–Apurímac (in South America), the Yangtze (in China), the Mississippi–Missouri–Red Rock (in the United States), and the Yenisey–Baikal–Selenga (in northern Asia).