Wakeford, Richard E., author
World Health Organization, 1974
Buku Teks
Abbatt, Fred, author
World Health Organization , 1980
Buku Teks
Mudd, Norma
Hodder & Stoughton Educational , 1998
Buku Teks
Celce-Murcia, Marianne, author
Cambridge University Press, 2011
Buku Teks
Rorden, Judith Waring, author
W.B. Saunders Company, 1987
Buku Teks