885-section5-9~~求解释

一加heidy

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
答案选E,就是因为要用将来时么，那E中的of是什么用法呢？