William & Wilkins, 1997
Buku Referensi
Byrd, Dani, author
Wiley-Blackwell, 2010
Buku Teks
Bryson, Bill, author
Penguin Books, 1987
Buku Referensi
edited by John Ayto
Helicon, 1994
Buku Referensi
Minkova, Donka, author
Cambridge University Press, 2009
eBooks