Which Group of Stars in the H-R Diagram Would Be

Multiple Choice

Which group of stars in the H-R diagram would be labeled "zero-age main sequence"?

A) stars that have just collapsed from the interstellar medium
B) stars that are just beginning to convert helium into carbon in their cores
C) stars that contain no processed elements (elements heavier than hydrogen or helium)
D) stars that have just started converting hydrogen to helium in their cores