题目内容

湿地保护和研究正在成为热点。人们逐渐接受的广义湿地概念革新了传统的地球环境分类系统。地球生物圈内生态系统的一级分类由海洋和陆地变成了海洋、湿地和陆地。湿地是三大生态系统中惟一的一个四圈（大气圈、水圈、土圈、岩石圈）交会的生态系统，与人类生存关系的密切程度令人吃惊。上面这段话主要支持了这样一种观点，即湿地保护和研究成为热点的原因是（）。

A. 湿地生态系统是具备气、水、土、石四圈交会的系统
B. 湿地地域广阔，革新了地球生物圈内的生态系统
C. 人类主要生活在湿地生态系统，与之关系最密切
D. 湿地生态系统生存条件恶劣，易发生各种自然灾害

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