Answer:
puberty
Explanation:
According to the scenario given, Marcia is sixteen years old and has already started menstruating and has added a few inches to her height and looks like a grown up, even though she isn't one yet.
Marcia is most probably experiencing puberty because she has started experiencing some changes synonymous with puberty such as menstruation, hormonal changes such as development of breasts which makes her look like a grown up and growth.
