Which of these is a district (Landkreis) in Brandenburg?

EDITORIAL LEARNING AID

Why is this answer correct?

Prignitz is a district in the north-west of Brandenburg. The Rhein-Sieg district lies in North Rhine-Westphalia, the Vogtland district in Saxony and the district of Amberg-Sulzbach in Bavaria.

Prignitz lies between the Elbe and Mecklenburg.

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