Duke University Press,
Majalah, Jurnal, Buletin
Short, Raymond W.
Henry Holt and Company, 1954
Buku Teks SO
Wachner, Clarence W.
Macmillan, 1963
Buku Teks SO
edited by Randall Stewart and Dorothy Bethurum
Scott, Foresman, 1954
Buku Teks SO
Kirby, David K.
Gale Research, 1975
Buku Referensi