English Department of Magister of Education Graduate School University of HKBP Nonmensen , 2015
Majalah, Jurnal, Buletin
edited by Keith and Helen Johnson
Blackwell, 1999
Buku Referensi
Julius Groos Verlag, {s.a}
Majalah, Jurnal, Buletin
Malmkjaer, Kirsten, editor
University Press, 2007
Buku Teks
selected and introduced by Roy Harris
Routledge/Thoemmes Press, 1995
Buku Referensi