Herring, E. Pendleton
McGraw-Hill, 1936
Buku Teks
Cooper, Phillip J.
Thomson Wadsworth, 2005
Buku Teks
Denhardt, Robert B.
Harcourt Brace College Publishers , 1999
Buku Teks
Weingand, Darlene E.
[American Library association, ], 2001
eBooks
Denhardt, Robert B.
Thomson, 2009
Buku Teks