APA-viite (7. p.)

(1994). Project learning tree: Environmental education activity guide (2nd.). Project Learning Tree.

Chicago-viite (17. p.)

Project Learning Tree: Environmental Education Activity Guide. 2nd. Washington: Project Learning Tree, 1994.

MLA-viite (9. p.)

Project Learning Tree: Environmental Education Activity Guide. 2nd. Project Learning Tree, 1994.

Varoitus: Nämä viitteet eivät aina ole täysin luotettavia.