Institute for Scientific co-coperation, [date of publication not identified]
Majalah, Jurnal, Buletin
edited by T. Marzuki Jacob
Universitas Sumatera Utara, 1994
Buku Referensi
Best, John W.
Pearson, 2014
Buku Teks
Best, John W., author
Prentice Hall of India, 1982
Buku Teks
Best, John W., author
Prentice-Hall, 1977
Buku Teks