Ward, A.C., author
Longman, 1955
Buku Teks
Williams, Harold Herbert, author
Sidgwick & Jackson, 1918
Buku Teks
Cambridge University Press, 2003
eBooks
Hewit, Douglas, author
Longman , 1988
Buku Teks
Cunliffe, John William, author
Books for Libraries Press, 1971
Buku Teks