Keeble, Richard, author
Routledge, 2007
Buku Referensi
Keeble, Richard, author
Routledge, 1994, 1944
Buku Teks
Edited by John A. Lent
The Iowa State University Press, 1971
Buku Teks
Stiles, Karl A., author
McGraw-Hill, 1968
Buku Referensi
edited by Martyn V. Twigg
Wolfe Publishing, 1989
Buku Referensi