Final answer:
The most useful theory for studying the long-term impact of adolescents' social media posts on their adult lives is Life Course Theory. It examines how experiences during adolescence can affect adulthood and accounts for the accumulation of experiences throughout an individual's life.
Step-by-step explanation:
The theory most useful for studying how adolescents' posts on social media affect them later in their adult lives is B) Life Course Theory. This theory is well-suited for examining the longitudinal impact of life events and experiences, including social media interactions. Life Course Theory provides a framework for understanding how experiences at one stage of life, like adolescence, can shape outcomes in later stages, such as adulthood. It takes into account the accumulation of social, psychological, and cultural experiences and their intricate effects throughout an individual's life.Social Exchange Theory is primarily associated with the idea that social behavior is the result of an exchange process to maximize benefits and minimize costs, but it doesn't quite fit the long-term developmental focus necessitated by the question. On the other hand, Family Stress Theory and the non-existent 'Alphabet Soup Theory' do not provide the longitudinal developmental framework that Life Course Theory offers.In conclusion, the Life Course Theory is the most relevant when considering the long-term effects of social media behaviors in adolescence on adult life outcomes.