39. Quasars---celestial objects so far away that their light takes at least 500 million years to reach Earth---have been seen since 1963. For anything that far away to appear from Earth the way quasars do, it would have to burn steadily at a rate that produces more light than 90 billion suns would produce. But nothing that burns at a rate that produces that much light could exist for more than about 100 million years. If the statements above are true, which one of the following must also be true on the basis of them? (A) Instruments in use before 1963 were not sensitive enough to permit quasars to be seen. (B) Light from quasars first began reaching Earth in 1963. (C) Anything that from Earth appears as bright as a quasar does must produce more light than would be produced by 90 billion suns. (D) Nothing that is as far from Earth as quasars are can continue to exist for more than about 100 million years.
(E) No quasar that has ever been seen from Earth exists any longer.
为什么这个是E呢？ | 
