Tripp, Charles
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Buku Teks SO
Alekseyev, A.
Foreign Languages Publishing House, 1955
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Dalton, George
Penguin Education, 1975
Buku Teks SO
Keat, Paul G.
Pearson Education (Prentice Hall), 2009
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Taylor, George A.
D. Van Nostrand, 1964
Buku Teks