Macmillan, 1981
Buku Referensi
Clark, Romy, author
Routledge, 1997
Buku Teks
Drake, Barbara, author
Harcourt Brace College, 1994
Buku Teks
Bramer, George R., author
Charles E. Merrill Publishing Company, 1981
Buku Teks
Trimmer, Joseph F., author
Houghton Mifflin , 1995
Buku Teks