Wilson, John B., author
Longmans Green , 1958
Buku Teks
Mulgan, John, author
Clarendon Press, 1967
Buku Teks
Evans, Ifor, Sir, author
Penguin Books, 1960
Buku Teks
Sampson, George, author
University Press, 1949
Buku Referensi
Lewis, Roy
Penguin Books, 1949
Buku Teks