In a certain city, the government is considering acquiring some land and turning it into a park (without any fences or gates). In an attempt to determine the extent to which residents of the city would value the park, residents are asked to fill out a questionnaire. Which of the following is correct?

a. On the questionnaire, some residents are likely to exaggerate the value they associate with the park.
b. On the questionnaire, some residents are likely to exaggerate the costs they associate with the park.
c. The use of such a questionnaire in cost-benefit analysis is likely to produce only rough approximations of residents' perceptions of the costs and benefits of a park.
d. All of the above are correct.