Answer:
d) the 20s and 30s segment
Step-by-step explanation:
The case clearly states "And the younger group has now passed the older segment in terms of the size of the population."
Besides the fact that there are more younger people than older people in the area, the demographic of the store's customers is changing also: "... sales of merchandise aimed at the younger customers have grown 30 percent, sales to the older crowd have been flat.".
We can imply that the store's largest market segment is young people in their 20s and 30s.