The most important advances made by man come from ______.

A．the development and the developing countries face a common problem
B．literacy is not a by-product of social and economic development
C．our view of literacy is very limited
D．illiterates constitute a large part of the world population

A．How to achieve literacy in their own countries.
B．How the environment can be changed to suit the people.
C．What methods of producing social and economic development can be found.
D．What ways of encouraging literacy as part of national development are possibl