= Solution
An old <globular cluster> has lost its original massive main-sequence members. Its <main-sequence turnoff> lies near a low stellar mass, typically around $0.8M_\odot$ for an age of order $10^{10}$ years. The diagram shows a lower <main sequence>, a <subgiant branch>, a prominent <red giant branch>, a <horizontal branch> of core-helium-burning stars, an <Asymptotic giant branch> and a faint <white dwarf> cooling sequence. The preceding schematic labels these features. A few <blue stragglers> may lie above the old turnoff because interaction or merger rejuvenated them; they do not imply a young age for the bulk population.
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