Why Are the Stars in an Open Cluster Useful for Studying

Why are the stars in an open cluster useful for studying just the early stages of stellar evolution?

A) These stars are all massive and thus erupt in a supernova explosion before the later stages of evolution are reached.
B) There are many different paths a star can take after the main sequence, and open clusters contain so few stars that each of these paths is followed by only a few stars, making them statistically unreliable for study.
C) The stars in an open cluster tend to dissipate after a few tens of millions of years and cease to be a part of the group.
D) These stars all tend to be very small, and after the early stages they begin to experience mass loss and disappear from view.