Barraclough, Geoffrey, 1908-1984
Penguin Books, 1967
Buku Teks
Keylor, William R., 1944-
Oxford University Press, 1996
Buku Teks
Palmer, Alan
Penguin Books , 1987
Buku Referensi
Grenville, J.A.S.
Routledge, 2005
Buku Teks
Shuter, Paul
Heineman Educational , 1988
Buku Teks