De Cecco, John P.
Prentice-Hall, 1974
Buku Teks
Greene, Judith
Open University Press, 2006
Buku Teks SO
edited Richard E. Ripple
Harper & Row , 1971
Buku Teks
Klausmeier, Herbert J.
Harper and Row, 1975
Buku Teks
Elliott, Stephen N.
McGraw-Hill, 2000
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