Passage Three

　　Public goods are those commodities whose enjoyment nobody can be effectively excluded. Everybody is free to enjoy the benefits of these commodities and one person’s use does not reduce the possibilities of anybody else’s enjoying the same good.

　　Examples of public goods are not as rare as one might expect. A flood control dam is a public good. Once the dam is built, all persons living in the area will benefit---regardless of their own contribution to the construction cost of the dam. The same holds true for highway signs or aids in navigation. Once a lighthouse is built, no ship of any nationality can be effectively excluded from use of the lighthouse for navigational purposes. National defence is another example. Even a person who voted against military costs or did not pay any taxes will benefit from the protection afforded.

　　It is no easy task to determine the social costs and social benefits associated with a public good. There is no practicable way of charging drivers for looking at highway signs, sailors for watching a lighthouse and citizens for the security provided to them through national defence. Because the market does not provide the necessary signals, economic study is to be replaced by the impersonal judgment of the marketplace.

　　26. What does the passage mainly discuss?

　　A. A specific group of commodities.

　　B. The economic structure of the marketplace.

　　C. Mechanism for safer navigation.

　　D. The advantage of lowering taxes.

　　27. Which of the following is NOT an example of a public good as described in the passage?

　　A. A stoplight. B. A bridge.

　　C. A fire truck. D. A taxicab.

　　28. The word “holds” in Line 4 of Paragraph 2 could best be replaced by __________.

　　A. has B. is

　　C. grasps D. carries

　　29. According to the passage, finding out the social costs of a public good is a _________.

　　A. matter of personal judgment

　　B. daily administrative duty

　　C. difficult procedure

　　D. citizen’s responsibility

　　30. Which of the following statements best describes the organization of the first two paragraphs?

　　A. A general concept is defined and then examples are given.

　　B. Generalizations are presented from which conclusions are drawn.

　　C. Persuasive language is used to argue against a popular idea.

　　D. Suggestions for the application of an economic concept are offered.