Why Are Star Clusters Almost Ideal "Laboratories" for Stellar Studies

Multiple Choice

Why are star clusters almost ideal "laboratories" for stellar studies?

A) All stars in the cluster are the same size and luminosity.
B) Their combined light makes them much easier to spot from a distance.
C) Stars in clusters have the same age, similar composition, and are at the same distance away.
D) Stars in clusters are all relatively young and therefore shine brightly.
E) Like our Sun, stars in clusters are always located in the plane of the Milky Way Galaxy.