Which Fact Referring to Stars in a Cluster Is NOT

Which fact referring to stars in a cluster is NOT particularly useful for interpreting the evolution of these stars?

A) The stars are all at the same distance from Earth, so we measure true intrinsic brightnesses of the stars.
B) The stars all formed at about the same time.
C) The stars formed from the same mix of chemical elements but with a mix of original masses.
D) The majority of the material in these stars is hydrogen.