**Core Concept**
This question tests the understanding of a randomized controlled trial (RCT), a type of clinical trial that is considered the gold standard in evaluating the efficacy and safety of a new treatment. In an RCT, participants are randomly assigned to either an intervention group (in this case, the new antihypertensive drug) or a control group (in this case, a placebo).

**Why the Correct Answer is Right**
The study described in the question is a classic example of a parallel-group RCT design. By randomly assigning patients to either the intervention or control group, the study aims to minimize bias and ensure that the groups are comparable in terms of demographics, clinical characteristics, and other factors that could affect the outcome. This allows researchers to estimate the effect of the new drug on blood pressure by comparing the mean blood pressure values between the two groups. The use of a placebo control group also helps to establish whether any observed effect is due to the active ingredient of the new drug.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because a case-control study would involve identifying patients with a specific outcome (e.g., high blood pressure) and then retrospectively examining their exposure to the new drug. This is not the design described in the question.
* **Option B:** This option is incorrect because a cross-sectional study would involve measuring blood pressure in a group of patients at a single point in time, without any follow-up or comparison to a control group. This is not the design described in the question.
* **Option C:** This option is incorrect because an observational study would involve observing patients in their natural environment, without any intervention or control group. This is not the design described in the question.

**Clinical Pearl / High-Yield Fact**
A key aspect of RCTs is the use of randomization to minimize bias and ensure that the groups are comparable. This is particularly important in studies of treatments for chronic conditions, such as hypertension, where there may be many potential confounding variables that could affect the outcome.

**Correct Answer: C. This study is an example of a parallel-group randomized controlled trial (RCT).**