单项选择题
A．大利另外，是否所有农民都没有受过教育，因此他们的产量都很低。 B．然而，如果所有农民都完全没有受过教育，那么他们的产品就会维持低水平。 C．从其它方面来看，假如所有的农民都不接受培训，他们的产品质量就会很差。 D．另一方面，如果所有的农夫都是文盲，他们的产量就不可能增加。
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．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