**Core Concept**
The question describes a sampling method where every fifth house is selected for a study, which is an example of a systematic sampling technique. This method involves selecting samples at regular intervals from a population, typically based on a specified sampling interval.

**Why the Correct Answer is Right**
The correct answer is a type of sampling method that involves selecting samples at regular intervals. In this case, every fifth house is selected, which means the sampling interval is 5. This systematic approach allows for a representative sample of the population to be obtained, which is essential for making inferences about the population as a whole.

**Why Each Wrong Option is Incorrect**
**Option A:** Random sampling - This is incorrect because random sampling involves selecting samples randomly from the population, whereas systematic sampling involves selecting samples at regular intervals.

**Option B:** Stratified sampling - This is incorrect because stratified sampling involves dividing the population into subgroups (strata) and then sampling from each subgroup, whereas systematic sampling involves selecting samples at regular intervals from the entire population.

**Option C:** Cluster sampling - This is incorrect because cluster sampling involves selecting clusters of the population (e.g., villages or schools) and then sampling from each cluster, whereas systematic sampling involves selecting samples at regular intervals from the entire population.

**Clinical Pearl / High-Yield Fact**
Systematic sampling is often used in observational studies and can be an efficient way to collect data from a large population, but it can also lead to biases if the sampling interval is not carefully chosen.

**Correct Answer: A. Random sampling - This is incorrect because random sampling involves selecting samples randomly from the population, whereas systematic sampling involves selecting samples at regular intervals.