这题没什么人问，想来是比较简单，但是我就是错了，希望NN们拉我一把，看看我的分析对不对 Astronomers at the Palomar Observatory have discovered a distant supernova explosion, one that they believe is a type previously unknown to science. (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） (E) they believe to be of OG的解释是：
Choice E is best. The pronoun that in A and B should be deleted, since the pronoun one is sufficient to introduce the modifier and the sentence is more fluid without that. In B and C, it and that it are intrusive and ungrammatical: the idiom is “believe x to be y.” In the context of this sentence, the infinitive to be is more appropriate than the limited present-tense is in referring to an event that occurred long ago but has been discovered only recently. Finally, A, B, and D lack of
and so illogically equate this particular explosion with the whole class of explosions to which it belongs: it is not a type but possibly one of a type.
they believe应该是个插入语，即使省略也不影响句子的整体意思，但是如果将A项中的that换为which是否就对了呢？ 另： E中的of后面是否有省略？ 或者此句是否是下面句子的变形呢？ which they believe is a type of previously unknown supernova explosion to science ===> E 中的one指代了此句中的 supernova explosion并提前，然后省略which？ 请NN们赐教！ | 
