What does the abbreviation CDU stand for in Germany?

EDITORIAL LEARNING AID

Why is this answer correct?

CDU stands for Christian Democratic Union; the party contests elections in all federal states except Bavaria, where its sister party CSU stands. The variants a, b and c are invented and are not party names.

CDU means Christian Democratic Union, sister party of the CSU.

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