Bowles, Chester
Africa's challenge to America / Chester Bowles
University Of California Press, 1956
 Buku Teks
LeBoeuf, Michael
The productivity challenge, how to make it work for america and you
McGraw-Hill, 1982
 Buku Teks
LeBoeuf, Michael
The productivity challenge how to make it work for America and you
McGraw-Hill, 1982
 Buku Teks
Fagen, Richard
Forging peace : the challenge of Central America / by Richard R Fagen
Blackwell, 1987
 Buku Teks
Politics in transitional societies : the challenge of change in Asia, Africa, and Latin America
edited by Harvey G. Kebschull
Appleton-Century-Crofts , 1968
 Buku Teks