edited by Ulrich Ammon, Norbert Dittmar, Klaus J. Mattheier
Walter de Gruyter, 1988
Buku Referensi
edited by Marvin J. Weber
CRC Press, 1995
Buku Referensi
Cambridge University Press, 2017
eBooks
Bolton, W. (William), 1933-, author
Nwenes, 1994
Buku Teks
Mc Graw Hill, 2007
Buku Referensi