**Core Concept**
The question is testing the understanding of statistical tests used for comparing ordinal data between two independent groups, particularly when the data does not follow a normal distribution. This involves knowledge of non-parametric tests, which are used when the assumptions of parametric tests are not met.

**Why the Correct Answer is Right**
Since the question is about ordinal data from two independent groups that are not normally distributed, the appropriate test would be a non-parametric test. The **Mann-Whitney U test** is commonly used for this purpose, as it can compare differences between two independent groups when the dependent variable is either ordinal or continuous, but not normally distributed.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because it doesn't specify a test that matches the criteria given in the question.
**Option B:** Similarly, this option does not align with the statistical test needed for ordinal data from two independent, non-normally distributed groups.
**Option C:** This option is also incorrect as it does not correspond to the appropriate statistical test for the given scenario.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that non-parametric tests like the Mann-Whitney U test are invaluable when dealing with data that doesn't meet the assumptions of normality required for parametric tests like the t-test.

**Correct Answer:** D. Mann-Whitney U test