Owen, W. V.
Ronald Press, 1958
Buku Teks
Davis, R.C., author
Harper & Row, 1951
Buku Teks
Certo, Samuel C.
Allyn and Bacon, 1989
Buku Teks
Assael, Henry
Kent Publishing Company, 1984
Buku Teks
Britt, Steuart Henderson, author
McGraw-Hill , 1968
Buku Teks