“Group of individuals of the same age” for a cohort refers to. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Survivorship curves summarize age-specific mortality: Type I concentrates loss late in life, Type II approximates a constant hazard, and Type III concentrates loss early. They are empirical patterns, not rigid taxonomic rules. The remaining alternatives—“Entire population”, “A single individual”, “Randomly selected population”—refer to different states, processes, or scales and therefore
Ref:
Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 10