阅读下面短文，在空白处填入1个适当的单词或括号内单词的正确形式。

Ecotourism has 【小题1】(it) origin with the environmental movement of the 1970s. It was not widely accepted as a travel concept 【小题2】 the late 1980s. During that time, increasing environmental awareness made it desirable.

Due to 【小题3】 growing popularity of environmentally-related and adventure travel, various types 【小题4】 trips are now being classified as ecotourism. Actually, a true eco-friendly trip must meet the following principles.