Which coat of arms belongs to the Free and Hanseatic City of Hamburg?

EDITORIAL LEARNING AID

Why is this answer correct?

The Hamburg coat of arms shows a white castle on a red background. Image 2 shows this coat of arms; the other images show coats of arms of other states or cities and are therefore wrong.

Hamburg: a white castle on a red background.

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