Geoffrey, Leech N.
Longmans, 1993
Buku Teks SO
Linguistic Analysis, 1996
Majalah, Jurnal, Buletin
Columbia : Columbia University Press and American Dialect Society
Majalah, Jurnal, Buletin
Artikel Jurnal
Bryant, Edward C.
McGraw-Hill, 1966
Buku Teks SO