Ramdas, Ganga P.
Westview Press, 1991
Buku Teks
Schneider, Gerhard W., author
Ronald , 1974
Buku Teks
editor, Gary Fromm
The Brookings Institution , 1971
Buku Referensi
Fayerweather, John
Prentice-Hall, 1965
Buku Teks
Maurer, Herrymon, author
Macmillan, 1956
Buku Teks