Buchanan, Robert Angus
Penguin, 1972
Buku Teks
Waldman, Don E.
Pearson, 2007
Buku Teks
Palmer, Marilyn
Routledge, 1998
Buku Teks
edited by Lyle F. Albright, Billy L. Crynes, William H. Corcoran
Academic Press, 1983
Buku Teks
Woodward, Joan
Oxford University Press, 1965
Buku Teks