Which present-day German federal state formerly belonged to the territory of the GDR?

EDITORIAL LEARNING AID

Why is this answer correct?

Thuringia lay in the Soviet occupation zone and was part of the GDR until 1990; the state was re-established in 1990. Hesse and Bavaria belonged to the American zone, Bremen to the American enclave on the Weser. All three were part of the Federal Republic.

Thuringia belonged to the GDR.

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