The correct answer is (a) Brussels.
The European Union (EU) is a political and economic union of 27 member states that are located primarily in Europe. The EU operates through a system of supranational institutions and intergovernmental-negotiated decisions by the member states. It aims to bring about the coordination of member states’ economic policies, a single market in which goods and people move freely, and common policies on trade, agriculture, fisheries, and regional development.
The EU was founded in 1957 with the signing of the Treaty of Rome by six countries: Belgium, France, Germany, Italy, Luxembourg, and the Netherlands. Since then, the EU has grown to include 27 member states, with Croatia being the most recent to join in 2013.
The EU’s headquarters are located in Brussels, Belgium. Brussels is also the seat of the European Parliament, the Council of the European Union, the European Commission, and the Court of Justice of the European Union.
The other options are incorrect because they are not the location of the EU’s headquarters. Helsinki is the capital of Finland, Paris is the capital of France, and Rome is the capital of Italy.