The Press of Case Western Reserve University, 1973
Buku Teks SO
Berkeley : The University of California
Majalah, Jurnal, Buletin
Spacks, Patricia Meyer
Wiley-Blackwell, 2009
Buku Teks SO
Plumb, John Harold, 1911-
Penguin Books, 1963
Buku Teks SO
Anderson, M.S.
Longman, 1971
Buku Teks SO