Lowell, Christopher, author
Discovery Books, 2000
Buku Teks
Rocknow, H.K., author
Stuttman, 1954
Buku Teks
Clifton-Mogg, Caroline, author
Pageone , 2001
Buku Referensi
A Ward Lock Book, 1997
Buku Referensi
Eckstut, Joann, author
Chronicle Books, 1999
Buku Referensi