City life and the state level belong together.
In a Berlin address, Berlin names the city. When you read about the House of Representatives or the Senate, you are reading about the parliament or government of the state of Berlin. You do not need to place another federal state above Berlin.
Brandenburg surrounds Berlin geographically. That does not mean Berlin is currently a city within the state of Brandenburg. The two states cooperate but remain separate federal states. A shared region does not automatically constitute a single state.

The other three answers
The other three named states are not city-states.
Saarland
Saarland is a federal state with several towns and municipalities. Its small area does not make it a city-state. Small and city-state are not synonyms.
Brandenburg
Brandenburg is the federal state surrounding Berlin. They are two states, however; Berlin’s location does not turn Brandenburg into a city-state.
Hessen
Hesse is also a federal state with several towns and municipalities. A major urban centre within a state does not make the whole state a city-state.
City-state does not mean an independent country outside Germany.
Berlin remains part of the Federal Republic and is bound by the Basic Law and federal legislation. The word state in city-state should not be confused here with a separate sovereign country outside Germany.
Hamburg and Bremen also count as German city-states; Bremen comprises the cities of Bremen and Bremerhaven. This test question offers only Berlin as a matching option. The original English question retains the German word Stadtstaat, which means city-state.
Article 1 · City and state · Constitution of Berlin ↗Berlin: city and state at the same time.
Geographically surrounded by Brandenburg, politically a separate federal state.
Three words for this question
- der Stadtstaatcity-state
- A federal state with an urban structure; in Berlin, city and state are combined.
- das Flächenlandterritorial state
- Here, a federal state that is not one of the three city-states.
- das Bundeslandfederal state
- A constituent state of the Federal Republic of Germany with its own state institutions.
