Final answer:
The Missouri River flows through North Dakota, South Dakota, and Missouri, eventually joining the Mississippi. It is the longest river in North America.
Step-by-step explanation:
The river that flows through North Dakota, South Dakota, and Missouri, eventually joining the Mississippi is the Missouri River. The Missouri River is the longest river in North America and is a major waterway in the central United States. It spans over 2,300 miles and is an important source of water for irrigation, transportation, and recreation.
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