Elections need people to carry out the practical work.
Election helpers serve on electoral boards and help voting and counting proceed correctly. Many volunteer. If there are too few volunteers, suitable eligible voters can be appointed.
The duties are performed in an honorary capacity. This differs from an ordinary employment relationship, but does not remove a statutory duty to accept. The catalogue’s English wording “voluntary office” should therefore not be understood as unrestricted freedom to ignore an appointment.

The other three answers
The other activities are not the election office carrying the duty described here.
club trainer
A club can request volunteer coaching. That does not create the statutory election duty meant in the question.
library supervisor
Library supervision can be paid or voluntary work. It is not the electoral office sought.
teacher
Teaching is a profession with its own requirements. Citizens are not required to become teachers through such a general request.
The duty has defined exceptions.
The Federal Electoral Regulations list, for example, particular family-care burdens, urgent work reasons, and illness or disability preventing proper performance of the duties. Under this rule, eligible voters who have reached age 67 on election day may also decline.
This explanation concerns federal elections. Other elections have their own applicable provisions. Whether a particular reason suffices must be clarified with the responsible office; the exam question does not decide an individual case.
Section 11 · Election office · Federal Elections Act ↗Election assistance: honorary office, general duty, important exceptions.
Distinguish volunteering from the consequences of a formal appointment.
Three words for this question
- das Wahlehrenamthonorary electoral office
- An honorary role in organising and carrying out an election.
- wahlberechtigteligible to vote
- Entitled to vote under the rules for the particular election.
- die Berufungappointment
- Formal appointment to a particular role.
