What applies to most children in Germany?

EDITORIAL LEARNING AID

Why is this answer correct?

School attendance is compulsory in Germany: children must attend school from a certain age, usually for nine or ten years. There is no compulsory voting (a), the duty of confidentiality (c) applies to certain professions, and compulsory religion (d) would contradict freedom of religion under Art. 4 GG.

Compulsory schooling yes, compulsory voting no.

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