DeLamater, John D.
Colorado Westview Press, 2014
Buku Teks
Pines, Ayala
McGraw-Hill, 1993
Buku Teks
Baron, Robert A.
Heights Allyn and Bacon , 1991
Buku Teks
Bonner, Hubert
American Book Company, 1953
Buku Teks
Baron, Robert A.
Pearson, 2009
Buku Teks