**Core Concept**
Stratified sampling is a type of sampling method where a population is divided into subgroups or strata based on relevant characteristics, and then a random sample is selected from each subgroup. This method ensures that each subgroup is adequately represented in the sample.

**Why the Correct Answer is Right**
Stratified sampling is used to reduce sampling error and increase the precision of the sample. By dividing the population into subgroups, researchers can ensure that the sample is representative of each subgroup, which is particularly useful when the population has a large variation in characteristics. This method is also useful when the population is heterogeneous and may not be adequately represented by a simple random sample.

**Why Each Wrong Option is Incorrect**
**Option A:** Simple random sampling is a method where a random sample is selected from the entire population, without dividing it into subgroups. This is not the correct answer because stratified sampling involves dividing the population into subgroups.
**Option B:** Cluster sampling is a method where a random sample of clusters or groups is selected from the population, and then a random sample is selected from each cluster. This is not the correct answer because stratified sampling involves dividing the population into subgroups, not clusters.
**Option C:** Systematic sampling is a method where a random sample is selected from the population at regular intervals, such as every 10th item. This is not the correct answer because stratified sampling involves dividing the population into subgroups, not selecting samples at regular intervals.
**Option D:** Convenience sampling is a method where a sample is selected based on ease of access or convenience, rather than random selection. This is not the correct answer because stratified sampling involves random selection from each subgroup.

**Clinical Pearl / High-Yield Fact**
Stratified sampling is particularly useful in epidemiological studies, where researchers need to ensure that the sample is representative of the population. By dividing the population into subgroups, researchers can identify patterns and trends that may not be apparent in a simple random sample.

**Correct Answer: C. Cluster sampling**