United Nations Environmental Program. (1987). State of the Environment: The state of the world environment. United Nations Environmental Program.
Cita Chicago (17th ed.)United Nations Environmental Program. State of the Environment: The State of the World Environment. Nairobi, Kenya: United Nations Environmental Program, 1987.
Cita MLA (9th ed.)United Nations Environmental Program. State of the Environment: The State of the World Environment. United Nations Environmental Program, 1987.
Atenció: Aquestes cites poden no estar 100% correctes.