Final answer:
The desire for autonomy is a major milestone of adolescence, allowing individuals to make and carry out their own decisions.
Step-by-step explanation:
The major milestone of adolescence being referred to in this question is autonomy, which is the desire and ability to make and carry out one's own decisions. Autonomy is a key component of self-identity development and is a significant task during adolescence according to Erikson's theory of psychosocial development. Adolescents go through a stage in which they start to question who they are and what they want to do with their lives. They try on different roles and explore their own interests and values, ultimately striving to establish a sense of self. The ability to make their own decisions and exercise autonomy is an important part of this development.