What is the accession of the GDR to the Federal Republic of Germany in 1990 generally called?

EDITORIAL LEARNING AID

Why is this answer correct?

The accession of the GDR to the Federal Republic on 3 October 1990 is called German reunification. NATO and EU eastern enlargement concern other states in eastern Europe, and "European Community" is the earlier name of the EU, not the name of this event.

3 October 1990 = German reunification.

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