Frolik, Lawrence A.
West Publishing , 2010
Buku Teks
Kapp, Marshall B.
Jones & Bartllett, 2010
Buku Teks
Scott-Kilvert, Ian
Longmans, Green, 1970
Buku Teks
Elder, Neil C.M.
Pergamon Press , 1970
Buku Teks
Witt, Elder
Congressional Quarterly, Inc., 1986
Buku Teks