Final answer:
The most marked fluctuations in self-image occur during young adolescence, a period of significant physical and psychological changes, including the development of personal identity and peer-based self-esteem(option c).
Step-by-step explanation:
Simmons and her colleagues found that the most marked fluctuations in self-image occur during c)young adolescence.
This stage of development is characterized by significant psychological and physical changes. Adolescence is a time when individuals go through puberty, experiencing sexual and physical maturation. Alongside these physical changes, adolescents develop a stronger sense of personal identity and the psychosocial changes include fluctuating self-esteem based on peer acceptance and other factors. The referenced study by Levy et al. (2002) also supports that how individuals perceive themselves, including their age identity, can have a profound impact on their well-being and even longevity.