Mason, Alpheus Thomas,1899-1989
Prentice-Hall, 1959
Buku Teks SO
Routledge, 2000
Buku Teks
Deutsch, Kenneth L.
Thomson, 2009
Buku Teks
Scott, Andrew M.
Holt, Rinehart & Winston, 1959
Buku Teks SO
Sharma, R.P.
Sterling Publishers Private, 1984
Buku Teks SO