Pfiffner, John M., author
Ronald Press, 1960
Buku Teks
Denhardt, Robert B., author
Harcourt College, 1999
Buku Teks
Herring, E. Pendleton, author
McGraw-Hill, 1936
Buku Teks
editor, Brian J. Rusbridge
Municipal Journal Limited, 1995
Buku Referensi
editor, Brian J. Rusbridge
Municipal Journal Limited, 1990
Buku Referensi