Starling, Grover, author
The Dorsey Press, 1982
Buku Teks
McKenna, George, author
McGraw-Hill, 1998
Buku Teks
Shea, John C.
St. Martin's Press, 1984
Buku Teks
Dolbeare, Kenneth M., author
D.C. Heath, 1985
Buku Teks
by William J. Keefe ... [and others]
The Dorsey Press, 1983
Buku Teks