Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.     Ecotourism is a unique way for travellers to engage in sustainable tourism while vacationing. This specific type of tourism is now increasingly becoming one of the more popular, with growth rates increasing every year. The United Nations, aware of the fact that tourism could be one of the most detrimental activities if not planned in accordance with the threshold imposed by nature, has declared the celebration of the International Day of Ecotourism, to promote sustainable practices in this growing industry.     Recently, The Division for Sustainable Development, Small Island Developing States Unit, decided that in preparation for the International Day of Ecotourism, it would be beneficial to identify successful practices of ecotourism on small islands. In order for ecotourism to be categorized as successful, it must meet the following criteria: it must combine natural and cultural tourism; it must involve local populations in the program, including providing educational resources to the local community, it must identity, manage and conserve the natural and cultural environment as well as the resources on the island; it must generate practices that will lead to the future sustainability of the island. If these criteria are followed by an "eco" organization, it deserves to be recognized as successful. 

What is the passage mainly about?