Consider the following statements about the European Union: I. The European Union was known earlier as the European Community. II. The Single European Act (1986) and the Maastricht Treaty were milestones in its formation. III. Citizens of European Union countries enjoy dual citizenship. IV. Switzerland is a member of the European Union. Which of the above statements are correct?

The correct answer is D because of the following reasons:

Statement I is correct. The European Union was officially established by the Maastricht Treaty in 1993, prior to which it was known as the European Community.

Statement II is correct. The Single European Act of 1986 prepared the ground for the free movement of goods and services, while the Maastricht Treaty of 1992 formally created the European Union and the concept of European citizenship.

Statement III is correct. Every person holding the nationality of a member state is also a citizen of the European Union. This constitutes a form of dual citizenship where EU citizenship complements national citizenship without replacing it.

Statement IV is incorrect. While Switzerland is part of the Schengen Area and has several bilateral agreements with the EU, it is not a member state of the European Union.

Since statements I, II, and III are true, option D is the correct choice.