## **Core Concept**
The question assesses the developmental milestone related to fine motor skills and hand-eye coordination in children, specifically the ability to construct a tower using cubes. This skill is a part of the Denver Developmental Screening Test and is used to evaluate the child's cognitive and motor development.

## **Why the Correct Answer is Right**
The ability to make a 3-cube tower is a developmental milestone that typically occurs around 15 to 18 months of age. At this stage, children have developed sufficient fine motor skills and hand-eye coordination to manipulate and stack cubes. This task requires precision and control, reflecting the child's advancing cognitive and motor abilities.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because making a 3-cube tower is not typically expected at the age mentioned (too early).
- **Option B:** This is the correct answer, so we skip it.
- **Option C:** This option is incorrect because it suggests an older age than typically required for this milestone.
- **Option D:** This option is incorrect for similar reasons as Option C, suggesting an even older age.

## **Clinical Pearl / High-Yield Fact**
A key developmental milestone is that by 15 months, a child should be able to stack 2 cubes, and by 18 months, they should be able to stack 3 cubes. This is a quick and useful test of fine motor skills during a pediatric assessment.

## **Correct Answer:** . 15-18 months.