根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项是多余的。
________71________It is a new term in today's tourism industry．But in an age of growing environmental awareness, it is not too difficult for us to imagine and understand this new form of holiday．
Ecotourism, which is considered as a kind of responsible tourism, is typically defined（定义）as travel to places where special and unusual plants, animals and cultural heritages （遗产） are the main attractions. _________72__________Therefore, programs concerning the protection of some natural and cultural spots also form a part of ecotourism．
