Making efforts to reach the height of mental maturity is the indication of

Developmental psychology divides the human lifespan into stages, infancy, early childhood, later childhood, adolescence, and adulthood, each marked by a distinct cognitive and psychological task. Adolescence (roughly 13 to 19 years) is defined as the transitional stage in which the individual actively works toward formal, abstract reasoning and a stable identity: an ongoing effort to rise from childlike thinking to adult-level mental maturity.

The stem describes exactly this ongoing striving, making efforts to reach the height of mental maturity, which is the hallmark developmental task of adolescence, not a state already reached or a capacity not yet developed.

• Adulthood: mental and psychological maturity is generally already established by this stage, so it describes an attained state rather than an ongoing striving.

• Early childhood (about 2 to 6 years): cognition is dominated by concrete, symbolic, and egocentric thought (Piaget's pre-operational stage), well before any capacity for abstract self-directed striving.

• Later childhood (about 6 to 12 years): reasoning becomes logical but stays tied to concrete objects and events (Piaget's concrete-operational stage), still short of the abstract striving described.

Result: the stem's description of an ongoing effort toward mental maturity therefore points to adolescence.