The cooperation of parties to form a government is called … in Germany

EDITORIAL LEARNING AID

Why is this answer correct?

When parties work together to form a government, this is called a coalition. A parliamentary group is the association of a party's members in parliament, a ministry is a government authority, and "unity" does not describe a form of government.

Parties cooperating to form a government = coalition.

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