According to the passage, public goods are ______.

单项选择题

It would be difficult to have a society like ours without public goods such as defense, transportation, and other services.
A public good is one that a person can use without reducing the use of it for another person. One of the best examples of a public good is national defense. One person can benefit from our national defense without reducing another person"s benefits. In fact, it is difficult to keep any person in our society from enjoying the benefits of national defense.
The market system does not work well in producing public goods. This is because a person who refuses to pay for a public good cannot be kept from using it. Suppose that the neighbors in a high crime area decide to hire a police force. Each neighbor, except Mrs. Smith, agrees to pay $100 a year for it. Mrs. Smith refuses to pay because she knows that if all the others pay the $100, the police will guard the area anyway. So Mrs. Smith can enjoy the services of the police force without paying $100.
The market system has no way to deal with this type of problem. For this reason, we cannot ask each person to make a direct payment in the form of product price. Therefore, we collect money for public goods by using taxes.

A．the products that we make for national defense
B．what we can buy and sell in public
C．the services enjoyed by all people
D．the taxes paid by the people involved