Wilkins, Lee
Lawrence Erlabum Associates, 2005
Buku Teks SO
Sommers, Christina
Harcourt Brace College Pub., 1997
Buku Teks SO
Weis, Gregory L
Prentice Hall, 1996
Buku Teks
Andrew I. Cohen: Christopher Health Well,am
Blackwell, 2005
Buku Teks SO
Hutabarat, Nadia Carolina
Universitas Indonesia, 2015
UI - Skripsi Membership