edited by Peter C. Smith, Laura Ginnelly and Mark Sculpher
Open University Press, 2005
Buku Teks
Clewer, Ann, author
Pearson Education, 1998
Buku Teks
Bodenheimer, Thomas S., author
Appleton & Lange, 1995
Buku Teks
edited by A.J. Culyer and K.G. Wright
Martin Robertson, 1978
Buku Teks
Mooney, Gavin H., author
Harvester Wheatsheaf, 1994
Buku Teks