单项选择题
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
A．there will be no safety if there is no national defense B．all the people should be responsible for national defense C．a public good is a shared benefit for the whole society D．some public goods are more important than others