Lawson, Edward, author
Taylor and Francis, 1991
Buku Referensi
Walmsley, D.J., author
Longman, 1993
Buku Teks
Praeger , 1991
Buku Teks
Wormer, Katherine Stuart van, author
Oxford University Press, 2017
Buku Teks
Hofer, Myron A
W.H. Freeman and Company , 1981
Buku Teks