Final answer:
Barbara is most likely exhibiting typical early adolescent behavior of focusing on popularity at the age of 13-15 years old, which is a common developmental stage for teenagers.
Step-by-step explanation:
Based on the context of the question, it appears that Barbara is exhibiting behaviors commonly associated with the teenage years, where social standings such as popularity become significant. Adolescents typically experience a heightened sense of social awareness and peer acceptance during their teenage years. The age group of 13-15 years old, which corresponds to early adolescence, is when many young people start to become more concerned with their social status and peer relationships. This developmental stage is characterized by a shift in focus from family to peers, and fitting in with friends often becomes a major concern.
The stress on being popular is often seen in the middle school years, which cover the ages of 13-15, aligning with option b. This age period is also when students are commonly in the 8th or 9th grade, which falls into the societal description of early teenagers, who are negotiating identity and self-concept alongside the physical and emotional changes of puberty. Therefore, the most likely age for Barbara's described behavior is within this age range.