USA : Macmillan, 1996,
Buku Referensi
prepared under the editorial supervision of In Plain English, Inc.
Macmillan, 1996
Buku Referensi
Ochs, Linnea Leedham
Prentice-Hall, 1987
Buku Referensi
Lippincott , 2004
Buku Teks
Bolander, Donald O.
Career Publishing, 1992
Buku Referensi