Rendell, Joan
Routledge & Kegan Paul , 1976
Buku Teks
Wals, Chad, author
Prentice-Hall, 1962
Buku Teks
Hilliard, Elizabeth, author
Conran Octopus Lim, 1996
Buku Referensi
hedges, Roy
Grolier International, 1999
Buku Teks
Hall, John W., author
McGraw-Hill, 1965
Buku Teks