Which of the following is not an example of developmental changes under…

Developmental change across the lifespan is classified into four broad patterns: change in size (increase or decrease), change in body proportion, disappearance of earlier/childhood features, and acquisition of new features -- the emergence of a structure or function that was not present before.

Applying this to each option:

• Permanent teeth erupt during childhood, physically replacing the milk teeth with an entirely new set of teeth -- a clear case of a new feature appearing.

• Primary sex characteristics mature and become functionally active around puberty; in the standard developmental classification used for this item, their emergence at puberty is grouped with the appearance of new features.

• Secondary sex characteristics (facial/body hair, voice change, breast development, and similar changes) appear for the first time at puberty and are the textbook example of acquisition of a new feature.

• The thymus gland follows the opposite pattern: it is largest in childhood and then undergoes progressive involution, shrinking after puberty -- a disappearance/regression, not the appearance of anything new.

Three options describe a new structure or function appearing, while only the thymus gland describes an existing structure regressing -- so the thymus gland is the one option that is NOT an example of acquisition of new features. This matches the official HTET 2024 Computer Science answer key.