Final answer:
Ending the French and German rivalry was essential to ensure lasting peace in Europe after World War II, which led to the creation of the European Economic Community (EEC) or Common Market to enhance economic cooperation.
Step-by-step explanation:
An important part of the Schuman Plan was to end the longstanding French and German rivalry because this was seen as vital to bringing lasting peace to Europe by preventing future conflicts and enhancing economic cooperation. Addressing the incompatibilities in political and economic systems, as well as foreign policy clashes, was critical in ensuring a stable and peaceful Europe. Similarly, the effort to unify Europe economically was greatly marked by the European Economic Community (EEC), also known as the Common Market, established in 1957 to ensure economic cooperation and prosperity among European nations post-World War II. European countries officially created a common market when they established the EEC. The answer to the question is therefore 'c. common market'.