Dorna, Mary
EM. Querido's Uitgeverij N.V, 1972
Buku Teks
Mersbergen, Jan van
Cossee, 2007
Buku Teks
Eckbo, Garrett, author
McGraw-Hill, 1969
Buku Teks
Martin, Chuck, author
American Management Association, 2007
eBooks
Downs, Frederick
W.W. Norton & Company, 1991
Buku Teks