Kimble, George H. T.
The Twentieth Century Fund, 1960
Buku Teks
Kimble, George H.T.
The Twentieth Century Fund, 1960
Buku Teks
Gay, Phillip T., author
McGraw-Hill, 2001
Buku Teks
Busia,K.A
United States of America, 1962
Buku Teks
edited by Colin M. Turnbull
Kingsport Press, 1973
Buku Teks