Final answer:
Cross-sectional research on fluid and crystallized intelligence supports the conclusion that fluid intelligence declines in late adulthood, while crystallized intelligence remains stable or improves.
Step-by-step explanation:
Crystallized intelligence refers to acquired knowledge and the ability to retrieve it, while fluid intelligence encompasses the ability to see complex relationships and solve problems.
Cross-sectional research on fluid and crystallized intelligence supports the conclusion that crystallized intelligence tends to hold steady as we age, and may even improve, while fluid intelligence declines in late adulthood. This decline in fluid intelligence can be delayed by engaging in mentally and physically stimulating activities.
Therefore, the conclusion drawn from cross-sectional research is that fluid and crystallized intelligence have different trajectories as we age, with crystallized intelligence remaining stable or improving, and fluid intelligence declining in late adulthood.