A park' s user fees are employed to maintain the park. When fewer people use the park, it suffers less wear. Thus raising user fees improves park maintenance even if the number of people who stop using the park because of higher fees is great enough to reduce the revenues devoted to maintenance. Which one of the following conforms most closely to the principle illustrated by the statements above? ['By spending more on zoo maintenance, a city increases the number of zoo patrons. The extra revenue generated by the sale of memorabilia more than makes up for the extra costs of maintenance.', 'Road taxes are raised to encourage more people to use mass transit. But since the fee paid by each commuter does not equal the cost of providing transit for that commuter, a mass transit service will deteriorate even as it takes in more money.', "To increase its market share, a car company improves the service warranty it provides to those who purchase a new car. Making good on the warranties proves expensive enough that the company's profits decrease even though its market share increases.", 'Library fees have been increased to raise money for book repair. Since the library now has fewer patrons, the books are in better repair even though the number of library patrons has decreased to such an extent that the money available for book repair has decreased.']