## **Core Concept**
This question assesses understanding of various sampling methods used in research, particularly in epidemiology and public health. Sampling methods are crucial for ensuring that a study's population is representative of the larger group being studied. The key concepts here involve understanding the definitions of different sampling techniques.

## **Why the Correct Answer is Right**
The correct answer, **Cluster Sampling**, is a method where the population is divided into clusters (in this case, schools), and a random sample of these clusters is selected. Then, either all members of the selected clusters or a random sample of members within each cluster are studied. Here, since 2 children are randomly selected from *every* school, it indicates a two-stage process where first, all schools are considered, and then a random sample of children from each is taken. This matches the definition of cluster sampling.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is blank and cannot be evaluated.
- **Option B:** This option is blank and cannot be evaluated.
- **Option C (Simple Random Sampling):** This involves selecting participants randomly from the entire population, giving each member an equal chance of being chosen. The scenario describes selecting children from every school, not randomly from the entire district population.
- **Option D:** This option is blank and cannot be evaluated.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that cluster sampling is often used for its practicality and cost-effectiveness, especially in large, dispersed populations. However, it may introduce bias if the clusters are not representative of the population. A classic example of cluster sampling is in the assessment of vaccination efficacy in different villages.

## **Correct Answer:** C. Cluster Sampling