what is the longest river in the north america?

Answer 1

The Mississippi River

Answer 2

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