Marshall, Geoffrey, author
Oxford University Press, 1957
Buku Teks
1977
Buku Teks
Lumb, R.D., author
Butterworth, 1974
Buku Teks
Foreign and Commonwealth Office
Her Majesty's Stationery Office, 1986
Buku Referensi
Austin, Dennis
Routledge , 1922
Buku Teks