**Core Concept**
Simple Random Sampling is a statistical method used to select a representative sample from a larger population. It involves randomly choosing participants without any bias or predetermination, ensuring that every individual in the population has an equal chance of being selected.

**Why the Correct Answer is Right**
In Simple Random Sampling, each member of the population is assigned a unique number or identifier, and a random number generator or random drawing is used to select participants. This process eliminates any selection bias, ensuring that the sample is representative of the population. The random selection process also helps to minimize sampling error and increases the reliability of the results.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because Stratified Random Sampling involves dividing the population into subgroups or strata and then randomly sampling from each subgroup. This method is used when the population is heterogeneous and there are distinct subgroups with different characteristics.
* **Option B:** This option is incorrect because Systematic Sampling involves selecting participants at regular intervals, such as every 10th participant. This method is used when the population is ordered in some way, such as by date or time.
* **Option C:** This option is incorrect because Cluster Sampling involves selecting a random sample of clusters or groups from the population, rather than individual participants. This method is used when the population is geographically dispersed or when it is difficult to access individual participants.

**Clinical Pearl / High-Yield Fact**
To ensure the validity of a sample, it's essential to use a random selection process, such as Simple Random Sampling, to avoid selection bias and ensure that the sample is representative of the population.

**Correct Answer:** D.