Wilkes, Angela
Passport Books, 1987
Buku Teks SO
Barratt, William B.
Aldine House, 1994
Buku Teks
Whitmarsh, W.F.H.
Longmans, Green, 1960
Buku Teks SO
Spencer, R.A.
Edward Arnold, [Date of publication not identified]
Buku Teks SO
Skaife, Linda
National Textbook Company, 1994
Buku Teks SO