Ritchie, J.B.
West Publshing Company, 1980
Buku Teks
Hatch, Mary Jo
Oxford University Press, 2013
Buku Teks
edited by Mason Haire
John Wiley & Sons, 1959
Buku Teks
Miles, Robert H.
Goodyear Publishing Company, 1980
Buku Teks
Morgan, Gareth
Sage Publications, 1986
Buku Teks