= Solution
The numbered features in the original <colour-magnitude diagram> have the following interpretation.
* \b[1:] the <main sequence>, where core <hydrogen> fusion supplies the <luminosity>; <stars> span a range of <masses> and <effective temperatures>.
* \b[2:] the <subgiant> region, following core <hydrogen> exhaustion, with a contracting helium-rich core and increasing hydrogen-shell burning.
* \b[3:] the <red giant branch>, with an extended cool envelope and a compact <helium> core fed by hydrogen-shell burning.
* \b[4:] the roughly horizontal core-helium-burning branch, or its red-clump part, reached after <helium> ignition; hydrogen-shell burning can continue outside the core.
* \b[5:] the white-dwarf cooling sequence, consisting of compact remnants supported mainly by <electron degeneracy pressure> and radiating stored <heat>.
Continuous <star> formation explains the coexistence of newly formed massive main-sequence <stars> with evolved low-mass remnants; interpreting a single sharp turnoff as the age of a coeval cluster would be inappropriate here.
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