Dyfyniad APA

Wang, H., & Whittington, D. (2000). Willingness to pay for air quality improvements in Sofia, Bulgaria. World Bank.

Dyfyniad Arddull Chicago

Wang, Hua, and Dale Whittington. Willingness to Pay for Air Quality Improvements in Sofia, Bulgaria. Washington, D.C: World Bank, 2000.

Dyfyniad MLA

Wang, Hua, and Dale Whittington. Willingness to Pay for Air Quality Improvements in Sofia, Bulgaria. World Bank, 2000.

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