9. 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. they believe to be of
1. 为什么不能是that 当先行词做定语从句的宾语，that 可以省略 one ( that ) they believe to be …….
2. 代词:it 多余。 One that they believe it to be / One that they believe that it is ……… believe 后面已经有逻辑宾语 one ,it 多余
3. 平行结构： A is B A/B 要平行对等， 此处 one(explosion ) is a type previously unknown to science. Explosion 不能是 a type. 可以是one of a type
4. 词法believe X to be Y / believe that ……
观点一to be比is在表示时间方面要好. 因为is是他们一直都这么认为, 时间概念太明确, 然而, TO BE就有模糊性, 所以这个题目里头OG说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.
观点二 这题偶的理解比较单纯，explosion, the one they believe to be of a type. 定语从句， 先行词还原到定语从句结构中就是： they believe the explosion to be of a type..... 根据believe 的两种用法： believe that ..... 和believe sth to be sth.....这里附和第二种用法。很自然的排除用限定性结构，（包括没有that, 直接用is 的结构。）
不过语言有很大的约定俗成的部分，即某种结构本身就带有某种含义。最好的办法是: 记住，形成习惯性思维，直到成为语感。看到某种结构就觉得应该是这个意思。 下列動詞接toV時總是用被動 allege, assume, claim, consider, deem, feel, find, know..., believe, ... 他們表示言談，想法或發現時，後面常接 to be 或 to have Vpp