## Core Concept
The question tests the understanding of a newborn's growth pattern, specifically the timeframe in which their birth weight quadruples. This is a basic yet important aspect of pediatric growth and development.

## Why the Correct Answer is Right
The average birth weight of a newborn is approximately 2.5 to 3.5 kg. A significant milestone in a child's growth is quadrupling their birth weight, which typically occurs by the age of 2 years. This growth pattern is crucial for pediatricians to assess the overall health and development of a child. By 2 years, most children have achieved this milestone, assuming normal growth rates.

## Why Each Wrong Option is Incorrect
- **Option A:** 1 year - Quadrupling of birth weight usually takes longer than 1 year. By 1 year, a child's weight is approximately 3 times their birth weight.
- **Option B:** 3 years - While growth continues beyond 2 years, quadrupling of birth weight typically happens before this age.
- **Option C:** 4 years - This is too late for quadrupling of birth weight; most children achieve this milestone much earlier.

## Clinical Pearl / High-Yield Fact
A key point to remember is that a child's birth weight roughly triples by 1 year of age and quadruples by 2 years of age. This is a simple yet critical benchmark for assessing growth and development in pediatric patients.

## Correct Answer: C. 2 years.