一个关于 one that的问题

记得在og上看到说当one和that都是代词的时候是不能同时出现的，那么这两道og上的题是怎么回事呢？

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）

(E) they believe to be of

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.

The proposed urban development zones do not represent a new principle; it was employed in “Operation Bootstrap” in Puerto Rico.

(A) do not represent a new principle; it

(B) represent not a new principle, but one that

(C) are not a new principle; the same one

(D) are not a new principle, but one that（B）

(E) are not new in principle; it

那位牛人给解释一下！感激不尽

第二个题的that做引导词吧

不是NN，但我的判断方法是：

前一个one在从句中做believe的宾语，所以可以省略that

后一个one在从句中做主语，所以不能省略that

可能只有that作为指示代词的时候才不能同时用吧，这两个列子THAT都是连词。

另外，第二题是OG上的吗，我怎么没见过呢，答案是哪一个呀？