edited by H. Thompson Prout, Douglas T. Brown
John Wiley & Sons, 2007
Buku Teks
London: Tiger Books International, 1994,
Buku Referensi
Austad, Carol Shaw
Jossey-Bass Publishers, 1996
Buku Teks
Guandola, M.H.
Merriam & Webster, INC, 1989
Buku Teks
1976
Buku Teks