Which of these is a borough of Hamburg?

EDITORIAL LEARNING AID

Why is this answer correct?

Altona is one of Hamburg's seven boroughs and lies west of the city centre. Hemelingen belongs to Bremen, Pankow to Berlin, and the Mecklenburg Lake District is a district in Mecklenburg-Vorpommern.

Altona is Hamburg, Hemelingen Bremen, Pankow Berlin.

This translation and explanation are editorial learning aids. The official German wording and answer key govern the examination.