what is the longest river in the north america?

Most sources claim the longest river is the Missouri.

http://www.enchantedlearning.com/usa/rivers/

http://www.worldatlas.com/webimage/countrys/nariv.htm

http://www.socialstudiesforkids.com/articles/geography/longestriversintheworld.htm

http://en.wikipedia.org/wiki/List_of_rivers_by_length#List_of_rivers_longer_than_1000_km

The longest river in North America is the Missouri River. However, if you consider the Missouri and Mississippi rivers as a combined system, then the longest river in North America would be the Mississippi River. To find this information, you can perform a simple search on the internet using a search engine like Google. Just type in "longest river in North America" and you'll find plenty of reliable sources that provide the answer.

The Mississippi River