OG12-45题，为什么不用过去时？

kenny1123

Quasars, at billions of light-years from Earth the most distant observable objects in the
      universe, believed to be the cores of galaxies in an early stage of development.

(A)  believed to be

(B)  are believed to be

(C)  some believe them to be

(D)  some believe they are

(E)   it is believed that they are
为什么不是were believed，不是在早期的时候吗？

Elroy

一般事实。现在时即可

心有林夕一点通

表示的意思是quasars正处在早期发展阶段而已。出现early不一定是过去。