Figure 19-11 of Universe, 11th Ed

Multiple Choice

Figure 19-11 of Universe, 11th ed., shows the evolution of a hypothetical open cluster. Is there a time when the most massive stars have become red giants and the least massive stars have not yet reached the main sequence?
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A) No, the protostar phase is so short compared to the main-sequence phase that all protostars have reached the main sequence long before any evolve off it.
B) No, the main-sequence phase is the longest, even for more massive stars, and all stars remain a great while on the main sequence before beginning evolution to red giants.
C) Yes, after about 30 million years for this cluster, there are both red giants and protostars.
D) Yes, after 1 billion years the least massive protostars have not yet reached the main sequence, while a few massive main-sequence stars have evolved to become red giants.