Van Matre, S., & Johnson, B. (1987). Earthkeepers: Four keys for helping young people live in harmony with the earth. Institute for Earth Education.
Citazione stile Chigago Style (17a edizione)Van Matre, Steve, e Bruce Johnson. Earthkeepers: Four Keys for Helping Young People Live in Harmony with the Earth. [Warrenville, Ill.]: Institute for Earth Education, 1987.
Citatione MLA (8a ed.)Van Matre, Steve, e Bruce Johnson. Earthkeepers: Four Keys for Helping Young People Live in Harmony with the Earth. Institute for Earth Education, 1987.
Attenzione: Queste citazioni potrebbero non essere precise al 100%.