Não informado. (2019). Statistical Yearbook. United Nations, Department of International Economic.
Chicago-referens (17:e uppl.)Não informado. Statistical Yearbook. New York: United Nations, Department of International Economic, 2019.
MLA-referens (8:e uppl.)Não informado. Statistical Yearbook. United Nations, Department of International Economic, 2019.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.