The Missouri River can be called a tributary because a tributary is a river or stream that flows into a larger body of water such as a river or lake. The Missouri River flows right into the Mississippi river and the Mississippi river flows into The Gulf of Mexico so that is why the Missouri River can be called a tributary.
Germany had an economic incentive to retake the Rhineland, because it is a mineral rich area. Your answer would be the third option. (c) Hope I helped out.
