APA

United States Environment Programme, . (2001). World Environment Day: 5 June 2001. [S.l.]: United Nations Environment Programme.

Chicago

United States Environment Programme, . 2001. World Environment Day: 5 June 2001. [S.l.]: United Nations Environment Programme.

Harvard

United States Environment Programme, . (2001). World Environment Day: 5 June 2001. [S.l.]: United Nations Environment Programme.

MLA

United States Environment Programme, . World Environment Day: 5 June 2001. [S.l.]: United Nations Environment Programme. 2001.