Reid, J. H. Stewart
Longmans, Green and Co. , 1959
Buku Teks
Iowa State University of Iowa 1956
Buku Teks
Hans Hagerdal, author
University of Indonesia, Faculty of Humanities, 2012
Artikel Jurnal
Longman Cheshire , 1992
Buku Teks
Winberg, Chai, author
Capricorn Books, 1974
Buku Teks