Downer, John
Sterling Pub. Co., 1999
Buku Referensi
Macmillan Press, 1978
Buku Teks
Perez-Cabal, Ma Angeles, editor
Wageningen Academic, 2011
eBooks
Poignant, Axel, author
Angus and Robertson, 1965
Buku Teks
Richard Francisco, author
Fakultas Ilmu Sosial dan Ilmu Politik Universitas Indonesia, 2017
UI - Tugas Akhir