Ammer, Karl
Halle Veb Verlag Sprache und Literatur 1961
Buku Teks
Hardisty, David
Oxford Oxford University Press 1989
Buku Teks
New York : The American Council on the Teaching of Foreign Language Inc
Majalah, Jurnal, Buletin
Batem
Monako : Marsu Productns, 2006
Buku Teks
Luneburg : Heliand-Verlag
Majalah, Jurnal, Buletin