For how many years is the Landtag in Saxony elected?

EDITORIAL LEARNING AID

Why is this answer correct?

The constitution of the Free State of Saxony sets a five-year electoral term for the Landtag. Three, four and six years are not electoral terms of the Saxon state parliament.

Saxony: Landtag five years, local elections from 18.

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