Hey Billy, (guessing that is your name)
I just did this problem. I felt confident with E mostly because I had crossed out each answer up to it.
Light from quasars take 500 million years to reach earth. And, in order for a celestial body that bright to be seen from earth, it must burn at the rate of 90 billion suns. The stimulus says that something that burns this strongly can only exist for 100 million years.
So, E correctly states that the quasar must not exist anymore, because if the light has been seen on earth, then it took 500 million years to get there, but the quasar itself can't live for more than 100 million years. Even though this celestial body ceased to exist, the light it created still traveled to the earth.
I hope I'm not wrong.