## Core Concept
The World Health Organization (WHO) defines various age groups for humans, and for adolescents, it specifies a particular age range that is critical for understanding growth, development, and healthcare needs.

## Why the Correct Answer is Right
The WHO defines **adolescence** as the period between 10 to 19 years of age. This age range is crucial for physical, psychological, and social development. During adolescence, individuals undergo significant changes that prepare them for adulthood. The correct answer reflects this definition.

## Why Each Wrong Option is Incorrect
* **Option A:** This option is incorrect because it does not accurately reflect the WHO's definition of adolescence.
* **Option B:** This option is incorrect as it suggests a broader or different age range not aligned with the WHO's specified definition.
* **Option D:** This option is incorrect because it provides an age range that does not match the WHO's criteria for adolescence.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the adolescent age range (10-19 years) is critical for healthcare providers, especially in preventive medicine and public health, as it is a period of significant growth and development. Interventions during this period can have long-term effects on health and well-being.

## Correct Answer: C. 10-19 years.