Mishan, E J
Penguin book, 967
Buku Teks
Gough, Ian, author
Macmillan, 1992
Buku Teks
edited and introduced by Andrew Shonfield and Stella Shaw
Heinemann Educational Books, 1972
Buku Teks
Robbins, Lionel, author
Macmillan, 1954
Buku Teks
Grove, J.M.
Longmans, 1962
Buku Teks