D.C. U.S. Department of Labor , 1957
Buku Teks
McDonald, Bryan L.
Oxford University Press, 2017
eBooks
Sethi, S. Prakash
Prentice-Hall, 1991
Buku Teks
Levesque, Roger J. R.
Oxford University Press, 2016
eBooks
Levitan, Sar A.
Harper & Row , 1982
Buku Teks