United Nations Conference on Environment and Development Rio de Janeiro, Brazil, World Travel & Tourism Council, World Tourism Organization, & Earth Council. (1992). Agenda 21 for the travel & tourism industry: Towards environmentally sustainable development. WTTC.
Lua i Stíl Chicago (17ú heag.)United Nations Conference on Environment and Development Rio de Janeiro, Brazil, World Travel & Tourism Council, World Tourism Organization, agus Earth Council. Agenda 21 for the Travel & Tourism Industry: Towards Environmentally Sustainable Development. [Brazil: WTTC, 1992.
Lua MLA (9ú heag.)United Nations Conference on Environment and Development Rio de Janeiro, Brazil, et al. Agenda 21 for the Travel & Tourism Industry: Towards Environmentally Sustainable Development. WTTC, 1992.