单项选择题
A．ensure the continuous supply of public goods B．reduce the difference between the rich and the poor C．get extra money to support public goods D．remind people of their duty
A．services enjoyed by all people B．what we can buy and sell in public C．products that we make for national defense D．taxes paid by the people involved
A．what role the market system plays in producing public goods B．how weak the market system is in producing public goods C．why some people refuse to pay for public goods D．what we can do to make use of the market system