Best, Robert
Longman Group Limited, 1986
Buku Teks
Potter, Simeon, author
Penguin Books, 1979
Buku Teks
Gerber, Philip L., author
Wadsworth , 1968
Buku Teks
Wear, George F.
Oxford University Press, 1950
Buku Teks
West, Michael
Longmans, Green and Co., 1951
Buku Teks