Artikel Jurnal
Fink, Arlene, author
Thousand Oaks : SAGE PUBLIKATION, 2003,
Buku Referensi
Wyatt, Wendy, author
Glorier International, 1999
Buku Referensi
Greene, Gardiner G., author
McGraw-Hill, 1975
Buku Teks
Humphries, john, author
Glorier International, 1999
Buku Referensi