Harbeck, Richard M.
Holt Rinehart and Winston, 1965
Buku Teks
Strickland, Warren L.
Burgess , 1964
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Marion, Jerry B.
Saunders College, 1982
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Athearn, Daniel
State University of New York, 1994
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Koperski, Jeffrey
Wiley Balckwell, 2015
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