Marks, John
Heinemann, 1983
Buku Teks SO
edited by R.C. Olby, G.N. Cantor, J.R.R. Christie and M.J.S. Hodge
Routledge, 1990
Buku Referensi
Merken, Melvin
Saunders College Publishing, 1993
Buku Teks SO
Robertson, Barry C.
John Wiley & Sons, 1981
Buku Teks SO
Holton, Gerald
Adison-Wesley, 1958
Buku Teks SO