For how many years is the Landtag in Thuringia elected?

EDITORIAL LEARNING AID

Why is this answer correct?

The Thuringian Landtag is elected for five years; this is laid down in the constitution of the Free State of Thuringia. Three, four and six years are not electoral terms of the Landtag.

Thuringia: Landtag five years, local elections from 16.

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