Não informado. (2008). School bell. National School Public Relations Association.
Παραπομπή σε μορφή Chicago (17η εκδ.)Não informado. School Bell. Washington: National School Public Relations Association, 2008.
Παραπομπή σε μορφή MLA (8th εκδ.)Não informado. School Bell. National School Public Relations Association, 2008.
Πρόσοχή: Οι παραπομπές μπορεί να μην είναι 100% ακριβείς.