A．Most of them would be indifferent and keep on throwing garbage into the fiver.
B．They would join the students in changing the situation.
C．They would become more aware of the pollution problem.
D．They would think twice before they went swimming or fishing in the fiver.

A．To outline contrasting types of economic systems.
B．To explain the science of economics.
C．To argue for the superiority of one economic system.
D．To compare barter and money exchange markets.