Barker, D.J.P.
Churchil Livingstone, 1976
Buku Teks SO
by James J. Nora [and others]
[publisher not identified], [date of publication not identified]
Buku Teks
James J. Nora [and others]
Lea & Febiger , 1993
Buku Teks SO
Blackman, Norman S.
Harwood Academic Publishers, 1990
Buku Referensi
Beyers, Marjorie
Little, Brown, 1984, 1984
Buku Teks SO