McAdams, Alan K., author
Columbia University Press , 1964
Buku Teks
Beirne, Joseph A., author
Prentice-Hall, 1969
Buku Teks
Widick, B.J.
Houghton Mifflin , 1964
Buku Teks
D.C. U.S. Department of Labor , 1957
Buku Teks
Paradis, Adrian A., author
Julian Messner , 1964
Buku Teks