You will be given a definition of a task first, then an example. Follow the example to solve a new instance of the task.
In this task you will be given an answer to a question. You need to generate a question. The answer given should be a correct answer for the generated question.

This list contains the top 25 accounts with the most followers on the social photo-sharing platform Instagram. As of May 2018, the most followed user is Instagram's own account, with over 235 million followers. Selena Gomez is the most followed individual, with over 137 million followers. Ten accounts have exceeded 100 million followers on the site.
Solution: who has the maximum number of followers on instagram
Why? The answer is talking about the Instagram accounts that have the most followers. The question asking about the maximum number of followers. So this is a good example.

New input: The Missouri makes a bend to the southeast as it winds through the Great Plains, receiving the Niobrara River and many smaller tributaries from the southwest. It then proceeds to form the boundary of South Dakota and Nebraska, then after being joined by the James River from the north, forms the Iowa -- Nebraska boundary. At Sioux City the Big Sioux River comes in from the north. The Missouri flows south to the city of Omaha where it receives its longest tributary, the Platte River, from the west. Downstream, it begins to define the Nebraska -- Missouri border, then flows between Missouri and Kansas. The Missouri swings east at Kansas City, where the Kansas River enters from the west, and so on into north-central Missouri. To the east of Kansas City, the Missouri receives, on the left side, the Grand River. It passes south of Columbia and receives the Osage and Gasconade Rivers from the south downstream of Jefferson City. The river then rounds the northern side of St. Louis to join the Mississippi River on the border between Missouri and Illinois.
Solution:
what river forms the border between iowa and nebraska