## Core Concept
The question pertains to the concept of population growth rates, specifically the classification of growth rates into different categories based on their annual percentage values. Understanding the different types of growth rates, such as exponential or 'explosive' growth, is crucial in demography and epidemiology.

## Why the Correct Answer is Right
An annual growth rate of 2-3% or more is often considered 'explosive' because it leads to a rapid doubling of the population in a relatively short period. For instance, a 2% annual growth rate means that the population will double in approximately 35 years, while a 3% growth rate will halve this doubling time to about 23 years. This rapid growth can put significant pressure on resources and infrastructure.

## Why Each Wrong Option is Incorrect
* **Option A:** Less than 1% is considered a low growth rate and does not lead to 'explosive' growth.
* **Option B:** 1-2% is a moderate growth rate but does not classify as 'explosive' compared to higher rates.
* **Option D:** More than 4% would indeed be very high, but the question asks for the range that represents 'explosive' growth, which is best described as 2-3%.

## Clinical Pearl / High-Yield Fact
A key point to remember is that even a 1% difference in annual growth rates can significantly affect population size over decades, illustrating the importance of understanding growth rates in public health planning.

## Correct Answer Line
**Correct Answer: C. 2-3%.**