Ovendale, Ritchie
Longman, 1993
Buku Teks
Milton-Edwards, Beverly, author
Routledge, 2003
Buku Teks
Cook, Chris, author
Longman, 1991
Buku Referensi
Walz, Jay, author
Atheneum, 1966
Buku Teks
Goldschmidt, Arthur, author
Westview Press, 1983
Buku Teks