Which river was not a part of the lousiana purchase? a. ohio river b. mississippi river c. arkansas river d. missouri river

It's between a and b.
The other three were part of the purchase. The history of the purchase says west of the Mississippi, but it is not clear to me whether or not the Mississippi was included or if it was just the boundary.

No account mentions the OHIO river, so I would pick that one. I'll check it. And I'm wrong.

The problem is the Mississippi which Spain controlled. They were tough negotiators and did not want to let go of their hold of the Mississippi River. The French didn't help much: they never defined what they were selling and America desperately needed the Mississippi to get its goods to Market. The OHIO valley needed the mississippi for the reason stated above, but it was not part of the purchase.

B  <<<<