Schaefer, Richard T
Pearson Education, 2015
Buku Teks
Pasaribu, Ruth Vania Christine
Fakultas Ilmu Pengetahuan dan Budaya Universitas Indonesia, 2014
UI - Skripsi (Membership)
Eljinah Anderson, editor ; Dougkas S. Massey, editor
Ruseel sage foundation, 2001
Buku Teks
Jaret, Charles
Harper Collins College Publishers, 1995
Buku Teks
Freedman, Amy L.
Routledge, 2000
Buku Teks