1.[B]【解析】that从句作名词doubt的同位语。doubt同时在there be结构中作主语。
2.[D]【解析】as引导非限制性定语从句,表达整个主句的意思,as在从句中作主语。
3.[B]【解析】so that...引导目的状语从句,相当于so as to bore或in order to bore。
4.[D]【解析】must have done表示从现在的角度对过去情况进行肯定的推测。
5.[A]【解析】other animals是被猎杀的对象,因此选择被动语态。另外,as well as连接两个对等成分,此处完整结构应为:“the elephant from being wiped out as well as other animals from being hunted in Africa.”from being与前文重复,可以省略。