This could be false. We don’t know anything about the instruments used to detect quasars, and whether it was their insensitivity that prevented quasars from being seen before 1963. It could have been some other factor—we don’t have enough information to know for sure.

This could be false. We don’t know why quasars were not seen from Earth before 1963. It could have been because their light didn’t reach Earth prior to 1963, or that we didn’t have the appropriate instruments to detect their light, or a number of other explanations.

This could be false. The 90 billion suns figure in the stimulus only applies to objects as bright and as far from Earth as quasars. The objects described in (C) may be closer to Earth than quasars and their brightness would not necessarily imply they produce that much light.

This could be false. The 100 million years figure in the stimulus only applies to objects as bright and as far from Earth as quasars. Objects described in (D) may be far less bright than quasars, and the stimulus doesn’t offer information about how long these objects can exist.

This must be true. By the time light from a quasar reaches Earth, 500+ million years would have passed. This is longer than any quasar’s ~100 million-year existence. Therefore, by the time its light reaches Earth, the quasar will have stopped existing.