Pioneer 10 and 11 Carried Plaques Intended to Show Any

Pioneer 10 and 11 carried plaques intended to show any alien civilization that found them the location of the solar system in the Galaxy.The location was marked relative to various pulsars (see Figure 15-10,Comins,Discovering the Essential Universe,6th ed.) .Which statement is a good reason to choose pulsars for this purpose?

A) Pulsars can be detected a long way across the Galaxy and thus presumably would be known to the aliens.
B) Pulsars can be identified uniquely by the frequencies of the radiation they emit.
C) Pulsar pulse rates are constant, never changing.
D) Pulsars form a more-or-less uniform ring around the galactic center (like the globular cluster halo) and thus provide a good coordinate system.