United Nations, 2004
Buku Teks SO
Herendeen, Robert A.
John Wiley & Sons, 1998
Buku Teks
Burns, Paul C.
Houghton Miffiln, 1984
Buku Teks
Reichman, Henry
[American Library association, American Library association], 2001
eBooks
edited by John Sears and Pete Sorensen
Routledge Falmer, 2000
Buku Teks SO