Emoto, Masaru, author
Beyond Words Pub, 2005
Buku Teks
Strecker, Edward A.
Macmillan, 1966
Buku Teks
Wonnacott, Ronald J., author
John Wiley & Sons, 1982
Buku Teks
Slipman, Sue
Pergamon Press, 1986
Buku Teks
Fritz, Roger, author
American Management Association, 2008
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