## **Core Concept**
The question assesses the developmental milestone of a child's fine motor skills and hand-eye coordination, specifically the ability to build a tower using cubes. This is a well-established assessment tool in pediatric psychology, reflecting a child's cognitive and motor development.

## **Why the Correct Answer is Right**
Building a tower of 9 cubes is a specific milestone that typically occurs around the age of 3 years. At this stage, children's fine motor skills have developed sufficiently to allow them to stack cubes in a more controlled and purposeful manner. The ability to build a tower of 9 cubes accurately reflects a child's hand function, coordination, and cognitive understanding of spatial relationships.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Typically, building a tower of 3 cubes is achieved around 15-18 months, which is much earlier than the milestone of 9 cubes.
- **Option B:** Building a tower of 6 cubes usually occurs around 2 years of age, which is still earlier than the milestone of 9 cubes.
- **Option D:** Building a tower of 12 cubes or more is usually achieved a bit later, around 3.5 to 4 years of age, making it too late for the specific milestone of 9 cubes.

## **Clinical Pearl / High-Yield Fact**
A commonly remembered sequence for cube tower building milestones is: 3 cubes by 15-18 months, 6 cubes by 2 years, 9 cubes by 3 years, and 12 cubes by 3.5-4 years. Remembering these milestones can help in assessing a child's developmental progress.

## **Correct Answer:** .