Meyer, Harold E., author
Prentice-Hall, 1992
Buku Referensi
Fruehling, Rosemary T., author
McGraw-Hill, 1994
Buku Teks
Marjo, Y.S., author
Setia Kawan, 2000
Buku Teks
Merriam-Webster's, Incorporated, 1993
Buku Referensi
Merriam-Webster, Inc., 1988
Buku Teks