## Core Concept
The core concept here involves determining the appropriate statistical test to assess the significance of changes in systolic blood pressure before and after the administration of an antihypertensive drug. This scenario involves paired or matched data, as the measurements are taken from the same subjects before and after treatment.

## Why the Correct Answer is Right
The correct answer, **Paired t-test**, is appropriate for this scenario because it is used to compare two population means where you have two samples in which observations in one sample can be paired with observations in the other sample. Here, the observations are paired as they come from the same patient (before and after treatment). The paired t-test calculates the difference between the two measurements for each patient, then tests if the average difference is significantly different from zero. This test assumes that the data follow a normal distribution, but it is robust for minor deviations.

## Why Each Wrong Option is Incorrect
- **Option A (Unpaired t-test):** This test is used to compare the means of two independent groups, not suitable here because the measurements are paired (from the same patients).
- **Option B (Mann-Whitney U test):** This is a non-parametric test used to compare two independent groups, which does not apply here since the data are paired.
- **Option D (Wilcoxon rank-sum test):** Similar to the Mann-Whitney U test, it is used for comparing two independent groups, not paired data.

## Clinical Pearl / High-Yield Fact
A key point to remember is that when dealing with paired data (e.g., before-and-after studies in the same subjects), paired tests (like the paired t-test or Wilcoxon signed-rank test) are more powerful and appropriate than unpaired tests. This is because they account for the individual variability and correlation between measurements.

## Correct Answer Line
**Correct Answer: C. Paired t-test**