Bryson, bill
Black Swan , 1998
Buku Teks
Kenyon, John Samuel, author
Merriam-Webster ; G. & C. Merriam Co., 1953
Buku Referensi
edited by Robert L. Chapman
Collins, 1989
Buku Referensi
edited by Frank O. Colby
Thomas Y. Crowell, 1950
Buku Referensi
Ciardi, John, author
Harper & Row , 1980
Buku Referensi