Vowels : J.P. Kelly and J.B. Heley
Majalah, Jurnal, Buletin
Columbia : Columbia University Press and American Dialect Society
Majalah, Jurnal, Buletin
Hardisty, David, author
Oxford Oxford University Press 1989
Buku Teks
New York : The American Council on the Teaching of Foreign Language Inc
Majalah, Jurnal, Buletin
Malang : Fakultas Pendidikan Bahasa dan Seni (FPBS)
Majalah, Jurnal, Buletin