求助!!两道GMAT语法题的区别

9. Astronomers at the Palomar Observatory have discovered a distant supernova explosion,one that they believe is a type previously unknown to science. 这里的one是指代前边的短语中的核心词explosion的，而后边的从句是修饰a distant supernova explosion整体的。应该是逻辑意思不对。下边的那个句子就没有这个问题。个人见解，欢迎拍砖
A. that they believe is
这题A答案错误
118.The World Wildlife Fund has declared that global warming, a phenomenon most scientists agree to be caused by human beings in burning fossil fuels, will create havoc among migratory birds by altering the environment in ways harmful to their habitats.
C. a phenomenon that most scientists agree is caused by human beings’ burning of fossil fuels,
?? 这题C选项正确
   个人觉得这两个选项一样呀，为啥一个正确，一个错误
   麻烦各位帮忙指点指点，3Q

谢谢你的回复哦~但我个人觉得one指代explosion和整个a distant supernova explosion没啥区别，因为a distant supernova explosion中，前面的修饰语都可以省略的，剩下中心语explosion。