## **Core Concept**
The question assesses knowledge of normal growth parameters in newborns, specifically head circumference. Head circumference is a critical indicator of brain growth and development in infants. It is measured in centimeters and is expected to follow a specific growth pattern.

## **Why the Correct Answer is Right**
The average head circumference at birth for a newborn is approximately 33-35 cm. The expected growth rate and final head circumference at a specific age can help determine if a child's development is on track. Typically, by 6 months of age, the average head circumference for an infant is about 43 cm. This growth reflects the rapid brain development that occurs during early infancy.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it suggests an unrealistic timeframe for achieving an optimal head circumference of 43 cm.
- **Option B:** This option does not align with the typical growth milestones for infants.
- **Option D:** This option suggests a later age than expected for achieving the specified head circumference, making it incorrect.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the head circumference of a newborn is expected to be around 33-35 cm at birth and should reach approximately 43 cm by 6 months of age. This growth parameter is crucial for assessing infant development.

## **Correct Answer:** C. 6 months.