The Location of the Galactic Center Was First Found by Harlow

Multiple Choice

The location of the Galactic center was first found by Harlow Shapley with

A) radio emissions from Sagittarius A.
B) Cepheids of population I in the spiral arms.
C) RR Lyrae variables in the globular clusters.
D) planetary nebulae in the open clusters.
E) infrared observations of the heat from its accretion disk around the black hole.