(1994). Project learning tree: Environmental education activity guide (2nd.). Project Learning Tree.
Citazione stile Chigago Style (17a edizione)Project Learning Tree: Environmental Education Activity Guide. 2nd. Washington: Project Learning Tree, 1994.
Citatione MLA (9a ed.)Project Learning Tree: Environmental Education Activity Guide. 2nd. Project Learning Tree, 1994.
Attenzione: Queste citazioni potrebbero non essere precise al 100%.