Merriam-Webster, 2004
Buku Referensi
Macmillan, 1994
Buku Referensi
edited by R.J. Johnston, Derek Gregory, Geraldine Pratt, Michael Watts
Blackwell Publishing, 2000
Buku Referensi
Henderson, I. F.
Longman, 1975
Buku Referensi
R & R Newkirk/Longman, 1985
Buku Referensi