Middle adulthood is the best choice that completes the statement. According to the Seattle Longitudinal Study, middle adulthood perceives to have the peak of mental abilities. However, there is an earlier decline of fluid intelligence compared to crystallized intelligence in this stage of development.
It increases the spending power of consumers and can increase aggregate demand, resulting in a higher economic growth
This gave america more culture such as jazz in the south and more people came to america which mean't more jobs, which mean't more currency for america. Hope i helped!
