Alexander, Kathie
Rockport Publishers, Inc., 2010
Buku Referensi
Watkins, L. H.
Prentice-Hall, 1981
Buku Teks
Gronlund, Norman E.
Allyn and Bacon, 1995
Buku Teks
Kumar, Anil
Tata McGraw-Hill,, 1981
Buku Teks
Llewelyn-Davies, R.
World Health Organization, 1966
Buku Teks