语法大全947- 145

applemusic

145.    #Astronomers at the Palomar Observatory have discovered a distant supernova explosion, one that they believe is a type previously unknown to science.（不明白）
(A) that they believe is
(B) that they believe it to be
(C) they believe that it is of
(D) they believe that is
(E) they believe to be of
就是不明白， 答案5

深海的小美人鱼

不明白在哪里？ 句子意思还是答案？

ca3ltoys

here should differ "it is..." from " it is of ...", different meaning. it's why A is wrong.
B. that they believe it to be, " it " is redundant
C. wordy and redundant
D. confused with " it is..." and " it is of..." too, and also wordy
E. the perfect answer, "one" here acts as the objects to "believe"

深海的小美人鱼

这个题的关键还是在believe to be of ..