Artikel Jurnal
Bone, Hugh A.
McGraw-Hill, 1981
Buku Teks SO
Fea, John
William B. Eerdmans , 2018
Buku Teks SO
by League of Women Voters of the United States
League of Women Voters of the United States 1961, 1962
Buku Teks
Stokes, Susan Carol
Cambridge University Press, 2014
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