Allen, R.G.D.
Macmillan, 1980
Buku Teks
Oparin, D.I.
Macmillan; Pergamon Press, 1963
Buku Teks
by United Nation
United Nations, 1991
Buku Teks
Her Majesty's Stationery Office, 1987
Buku Referensi
Blades, Derek W.
Development Centre of the Organisation for Economic Co-operation and Development, 1974
Buku Teks