Wilson, Arthur
Longman, 1966
Buku Teks
Asean University Network,
Majalah, Jurnal, Buletin
Titherington, D.
McGraw-Hill, McGraw-Hill, 1982
Buku Teks
Faculty of science & engineering Waseda University, 2007
Majalah, Jurnal, Buletin
Bolton, William, 1933-
Nwenes, 1994
Buku Teks SO