Tambunan, author
Kementerian PPN/Bappenas, 2018
Artikel Jurnal
Tarrant, Naomi
London Routledge 1994, 1994
Buku Teks
Curtis, Helena
Worth Publishers, 1972
Buku Teks
Helena Olii, author
Indeks, 2007
Buku Teks
Stungo, Naomi
Carlton Books, 2002
Buku Teks