Answer:
a. achieving stage.
Step-by-step explanation:
Warner Schaie is a developmental German psychologist who has focused on the cognitive stages of people along their lifespan.
According to him, people go through different stages of cognitive development (since childhood and until they are old) along their life span.
The Achievement stage is the second stage of his theory and it takes place in young adulthood, according to Schaie during this stage the individual's primary cognitive tasks are to achieve personal goals in the long term future (starting a family, being successful in their careers, make contributions to society) by applying the intellectual skills that they learned when they were younger (adolescents).