**Core Concept**
The increase in height of a child from 1 to 3 years is a critical period of growth and development. During this stage, the child experiences a rapid increase in height due to the proliferation and differentiation of chondrocytes in the growth plates of long bones. This process is regulated by a complex interplay of hormones, including growth hormone and thyroid hormone.

**Why the Correct Answer is Right**
The correct answer is related to the percentage increase in height during this period. From 1 to 3 years, the average child experiences a 50% increase in height. This is because the growth rate during this period is relatively constant, with a small percentage increase in height each year. The growth plates in the long bones are responsible for this rapid increase in height, as they allow for the elongation of the bones through the addition of new chondrocytes.

**Why Each Wrong Option is Incorrect**
**Option A:** 25% - This is an underestimate of the actual increase in height during this period.
**Option B:** 75% - This is an overestimate of the actual increase in height during this period.
**Option C:** 100% - This is an overestimate of the actual increase in height during this period, as it would imply a complete doubling of the child's height.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the growth rate of children varies significantly during different periods of development. From 1 to 3 years, the growth rate is relatively constant, but it slows down significantly after 3 years, accelerating again during puberty.

**Correct Answer: D. 50%**