British Council , 1998
Buku Teks
Ritchie, Charles
Macmillan of Canada, 1974
Buku Teks
ASEAN Secretariat
ASEAN Secretariat, 1987
Buku Referensi
Stevens, Barbara J.
Aspen Publication, 1983
Buku Teks
Vihman, Marilyn May, author
Wiley-Blackwell, 2014
Buku Teks