Where is the headquarters of the EU?
1. Rome
2. Geneva
3. Berlin
4. Brussels

Hint: The European Union or the EU is a union of 27 member countries located in Europe, dealing with political and economic affairs. It is headquartered in the capital city of Belgium.

Complete answer: Let us have a look at the options given:
Option 1: The treaty that established the European Economic Community (EEC) was signed in the city of Rome. The EEC was an important step in the creation of the European Union. However, it cannot claim to be its headquarters. Thus, it is not the correct option.
Option 2: Geneva is a city of Switzerland. Though Switzerland maintains cordial relations with the European Union, it is not a member state. So, there is no question of it being the headquarters of the EU.
Option 3: Berlin is the capital of Germany. It forms an integral part of the Union and has a representation of 96 members in the European Parliament. However, it is not the headquarters of the EU. Hence, this is an incorrect option.
Option 4: Brussels is the capital of Belgium. It is said to be the de facto capital of the EU. It hosts a number of EU institutions. Thus, it is the correct option.

Therefore, the correct answer is option 4.

Note: The European Union does not have an official capital. However, Brussels is considered to be the headquarters because of its sheer predominance in terms of the number of EU institutions that it hosts.