Cochrane, James C.
David & Charles , 2008
Buku Teks SO
Ziegler, Kathleen
Rockport Publishers, 1994
Buku Referensi
Shannon, Faith
Reed International Books, 1987
Buku Referensi
Lafosse, Michael G.
Quarry Books, 1998
Buku Referensi
Universitas Indonesia, 1987
UI - Tugas Akhir