Quasars, at billions of light-years from Earth the most distant observable objects in the universe, (B) are believed to be the cores of galaxies in an early stage of development.
想请问 这个句子未划线部分: Quasars 的两个同位语之间为和没有"," 连接?
at billions of light-years from Earth
the most distant observable objects in the universe,
at billions of light-years from Earth and in the universe are two prepositional phrases in a appositive phrase. A comma is not really needed to seperate them two. For instance, Danny works in a shop at the Heathrow Airport.