2Peter E Murphy. Tourism and Sustainable Development [A]. William F. Theobald - edited, Global Tourism: The Next Decade [ C ]. New York; Butterworth - Heinemann Ltd, 1994.
3Lee D N B, Snepenger D J. An Ecotourism Assessment of Tortuero [ J ]. Costa Rica, 1992,19 ( 2 ): 367 - 370.
