Higgins, Hugh
Heinemann Educational, 1975
Buku Teks SO
Woon, Park Seung
Fakultas Ilmu Pengetahuan Budaya Universitas Indonesia, 2018
UI - Skripsi Membership
Sumarno
2010
UI - Skripsi Open
editor in chief, Stanley I. Kutler
Charles Scribner's Sons, 1996
Buku Referensi
Bodard, Lucien
Atlantic Monthly Press Book, 1967
Buku Teks SO