1.
2.
3.
New York : United Nations, Dept. of Public Information, 1986.
Tenth edition.
Italian | C 23 UN.E |
4.
5.
6.
[Washington, D.C.] : World Resources Institute in cooperation with United Nations Environment Programme, the World Conservation Union, 1995.
Spanish | G 26 NAT |
7.
8.
9.
10.