Evans, G.O.
Taylor and Francis, 2009
Buku Teks SO
Japan Society for the Promotion of Science, 1882
Buku Referensi
Indonesia Scholars Journal, 2016
Majalah, Jurnal, Buletin
Goulding, Christina
Sage, 2002
Buku Teks
Robson, Colin
Oxford, 2002
Buku Teks SO