Which of the following lists contains only federal states that belonged to the territory of the former GDR?

EDITORIAL LEARNING AID

Why is this answer correct?

The GDR consisted of the five states of Mecklenburg-Western Pomerania, Brandenburg, Saxony, Saxony-Anhalt and Thuringia, plus East Berlin. These states acceded to the Federal Republic in 1990. Lower Saxony, North Rhine-Westphalia, Hesse, Schleswig-Holstein, Bavaria, Baden-Württemberg and Rhineland-Palatinate belonged to the old Federal Republic, so the other lists each contain West German states.

Only MV, Brandenburg, Saxony, Saxony-Anhalt and Thuringia belonged to the GDR.

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