According to Esther Thelen, motor behaviors are assembled for perceiving and acting. Her theory is called

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theory.

A. Phenylketonuria (PKU): PKU is an inherited metabolic (single-gene) disorder and is not related to maternal age in the way chromosomal nondisjunction is.
B. Down syndrome: Down syndrome (trisomy 21) risk increases markedly with maternal age; it occurs far less often in births to mothers aged 16–34 than in older mothers.
C. Turner syndrome: Turner syndrome results from monosomy X (missing X) and is not strongly linked to maternal age in the same way as trisomy 21.
D. Sickle-cell anemia: Sickle-cell anemia is an inherited single-gene disorder (autosomal recessive) tied to parental carrier status, not maternal age.

A. Identity foreclosure: Foreclosure is commitment without prior crisis/exploration, so it does not fit someone who has undergone a crisis.
B. Identity diffusion: Diffusion is marked by neither crisis nor commitment, so it contradicts the description.
C. Identity achievement: Identity achievement is reached after a period of crisis/exploration followed by making a committed choice; this matches “undergone a crisis and made a commitment.”
D. Identity moratorium: Moratorium indicates active exploration/crisis without having yet made a commitment, so it does not fit someone who has already made a commitment.