Question

nearby quasars are rare because
○ galaxies located relatively close to the milky way are not of the correct type and are not able to power a quasar
○ they can only be seen at great distances because they are very luminous.
○ they existed during an earlier period of the universe and so today must be located at great distances.
○ they only exist in galaxies that formed most recently and these galaxies are also located at the greatest distances.

Explanation:

Quasars are extremely luminous objects that were more common in the early - universe. Since light takes time to travel, the light from these early - universe quasars has taken a long time to reach us, so they are located at great distances. They are less likely to be nearby as they existed in an earlier cosmic epoch.

Answer:

they existed during an earlier period of the Universe and so today must be located at great distances.