**Core Concept**
Randomization is a fundamental aspect of clinical trials, ensuring that the participants are divided into groups in a way that minimizes bias and allows for a comparison of the outcomes between groups. This process helps to eliminate confounding variables and ensures that the groups are comparable, making it easier to attribute differences in outcomes to the intervention being studied.

**Why the Correct Answer is Right**
The primary purpose of randomization is to reduce selection bias and ensure that the groups are equivalent in terms of known and unknown confounders. This is achieved by using a random process to allocate participants to either the intervention or control group. By doing so, randomization helps to create groups that are similar in terms of demographics, baseline characteristics, and other factors that could influence the outcome. This allows researchers to draw valid conclusions about the effectiveness of the intervention being studied.

**Why Each Wrong Option is Incorrect**
**Option A:** Randomization is not primarily used to reduce selection bias, although it does help in that regard.
**Option B:** While randomization can help to eliminate confounding variables, it is not its primary purpose.
**Option C:** Randomization does not involve assigning participants to groups based on their baseline characteristics.

**Clinical Pearl / High-Yield Fact**
A key principle of randomization is that it should be performed by an independent person, not by the researcher or study personnel, to maintain the integrity of the trial.

**Correct Answer: D. To reduce selection bias and ensure that the groups are equivalent in terms of known and unknown confounders.**