Werbach, Melvyn R.
Thorsons, 1993
Buku Referensi
Heinerman, John
Prentice Hall, Paramus, N.J., 1998
Buku Teks SO
Murray, Michael T.
Three Rivers Press, 1996
Buku Teks SO
Stevenson, Gladys T.
John Wiley & Sons, 1960
Buku Teks SO
Stokes, Adrian V.
Wildwood House, 1986
Buku Referensi