**Core Concept**
The concept being tested here is fetal growth and development, specifically the rate at which a newborn's birth weight doubles. This is a critical aspect of pediatric medicine, as understanding normal growth patterns helps clinicians identify and manage potential growth disorders or developmental delays.

**Why the Correct Answer is Right**
The birth weight of a newborn baby doubles by approximately 5-6 months of age. This rapid growth phase is due to the baby's increasing caloric intake from breast milk or formula, as well as the maturation of digestive enzymes and the gut. The rate of growth is influenced by genetic factors, as well as maternal nutrition and overall health.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it implies an unrealistic rate of growth, exceeding the normal doubling time.
**Option B:** This option is incorrect because it suggests the doubling time is much shorter than the actual rate, which may lead to overestimation of growth potential.
**Option C:** This option is incorrect because it implies the doubling time is much longer than the actual rate, which may lead to underestimation of growth potential.

**Clinical Pearl / High-Yield Fact**
A useful mnemonic to remember the doubling time is "5-6 months, that's the pace," emphasizing the importance of regular growth monitoring in pediatric patients.

**Correct Answer:** C. 5-6 months