Williams, Carolyn L.
American Psychological Association , 2011
Buku Teks
Wallis, W.D.
Springer, 2012
eBooks
Stapleton, Gerald F.
Tab Books, 1971
Buku Referensi
Ward, Brice
Blue Ridge Summit TAB Books , 1971
Buku Teks
Schildt, Herbert
McGraw-Hill, 2012
Buku Teks