United Nations Environment Programme Industry and Environment. (1998). Ecolabels in the tourism industry. UNEP.
芝加哥风格引文United Nations Environment Programme Industry and Environment. Ecolabels in the Tourism Industry. Paris, France: UNEP, 1998.
MLA引文United Nations Environment Programme Industry and Environment. Ecolabels in the Tourism Industry. UNEP, 1998.
警告：这些引文格式不一定是100％准确.