Katrina Brown ... [et al.]
The Global Environment Facility, 1993
Buku Teks
Crystal, David, 1941-
Cambridge University Press , 2007
Buku Teks SO
Levinson, Stephen C.
Cambridge University Press, 2004
Buku Teks
Monika Unkel
Graduate School of Language and Culture, Osaka University, 2018
Artikel Jurnal
Kalbe, 2006
Buku Teks SO