## **Core Concept**
The question pertains to the developmental milestone of brain growth in humans. Brain growth is a critical aspect of human development, especially during early childhood. Understanding the timeline of brain development is essential for pediatricians and developmental specialists.

## **Why the Correct Answer is Right**
The correct answer, , signifies that 90% of brain growth is achieved by the age of 3 years. This period is crucial for cognitive, motor, and language development. Rapid brain growth during early childhood lays the foundation for future learning and development. Research indicates that significant neural development and maturation occur in the first few years of life, with a marked deceleration in the rate of growth after this period.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not accurately represent the age by which 90% of brain growth is achieved.
- **Option B:** This option is incorrect because it suggests a later age, which does not align with the established developmental milestone of 90% brain growth achievement.
- **Option D:** This option is incorrect as it implies an even later age, which is beyond the critical period of rapid brain growth.

## **Clinical Pearl / High-Yield Fact**
A critical point to remember is that early childhood, particularly the first three years, is a window of opportunity for brain development. Interventions and environmental stimuli during this period can significantly impact cognitive and motor skills development. This concept is often emphasized in pediatric education and is a high-yield fact for exams.

## **Correct Answer:** .