语法分册第33页的第9道

寂寞的自由

14．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

这个大家帮忙分析一下，特别是对于E的取舍原因，还有一个笨笨的问题，就是定语从句中的关系代词THAT，如果在定语从句中THAT做宾语，那么THAT可以省略吗（TOEFL中可以，不知道GMAT里的规则是怎样的，谢谢大家）

天山

在GMAT规则中，宾语从句的that 不能省略，但是one 后面不能带that.
ETS尽管一再强调这一规则，但是在非划线部分的宾语从句中，它自己也常常 省略了that, 这就叫：只许州官放火，不许百姓点灯。 这中情况当然也不能说它错了。
且（e)  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.