Which of the following countries was NOT an original member of the European Common Market?

When the European Common Market was formed March 25th 1957 Germany, Italy and Belgium were all included. Spain did not become a member until January 1st 1986.

In 1957 six core states founded the EU's predecessor, the European Economic Community. The remaining states have acceded in subsequent enlargements. On 1 July 2013 Croatia became the newest member state of the EU. In order to accede, a state must fulfill the economic and political requirements known as the Copenhagen criteria, which require a candidate to have a democratic, free market government together with the corresponding freedoms and institutions, and respect for the rule of law. Enlargement of the Union is also contingent upon the consent of all existing members and the candidate's adoption of the existing body of EU law.