Final answer:
Anushka's move from sales to management aligns with her accumulated knowledge and experience, as crystallized intelligence remains steady or improves with age, as opposed to fluid intelligence which declines.
Step-by-step explanation:
Anushka's career shift from a pharmaceutical salesperson to a regional manager is better explained by C. Accumulated knowledge and experience. This is because, as we age, our crystallized intelligence, which encompasses the skills and knowledge we've gained over time, tends to remain stable or improve. However, we do begin to see a decline in fluid intelligence, such as information processing abilities and memory, which can impede the quick-wittedness required in sales roles. Therefore, the cognitive changes that best explain this age-related shift in Anushka's career are her accumulated knowledge and experiences over the years, allowing for expertise in her field and a new role that leverages this strength.