## Core Concept
The question pertains to a specific type of sampling technique used in research and statistics. Sampling techniques are methods used to select a subset of individuals or units from a larger population, aiming to accurately represent the population. The technique described involves selecting every 10th unit from the population.

## Why the Correct Answer is Right
This type of sampling technique, where every nth unit is chosen from the population, is known as **Systematic Sampling**. In systematic sampling, a random starting point is selected, and then every nth member from the list is chosen. For example, if a researcher wants to sample 1,000 people from a population of 10,000 using systematic sampling with a sampling interval (n) of 10, they would select every 10th person from the list after a random start. This method ensures that the sample is spread across the population, reducing bias.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is not provided, but typically, incorrect options might include other types of sampling techniques such as simple random sampling, cluster sampling, or stratified sampling, which do not involve selecting samples at regular intervals.
- **Option B:** Similarly, without the specific text, we can infer that if it's not systematic sampling, it might refer to a technique like **Simple Random Sampling**, where every member of the population has an equal chance of being selected, but it's not based on a fixed interval.
- **Option C:** This could potentially refer to **Stratified Sampling**, where the population is divided into distinct subgroups (strata) and then a simple random sample is selected from each stratum. It doesn't involve selecting every nth unit.
- **Option D:** Without specifics, if this isn't systematic sampling, it could refer to **Cluster Sampling**, where the population is divided into clusters, and a random selection of these clusters is chosen for the sample. This also doesn't involve a systematic interval.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **systematic sampling** is useful for large populations where a complete list is available, and it provides a spread across the population. However, it's crucial to ensure there's no underlying pattern in the list that could bias the sample (e.g., alphabetical order by name might inadvertently sample only one gender or age group if not properly randomized).

## Correct Answer: C. Systematic Sampling