Higgins, Alex
McGraw-Hill Book Company, Inc., 1945
Buku Teks
Chattopadhyay, P., author
McGraw-Hill, 2001
Buku Teks
Hollins, Carole, author
Blackwell Munksgaard, 2006
Buku Teks
Boyd, William E., author
Prentice-Hall, 1955
Buku Teks
Leal, A.L.
Longman, 1978
Buku Teks