**Core Concept**
A case-control study is a type of observational research design that involves comparing individuals with a specific outcome or disease (cases) with individuals without the outcome or disease (controls) to identify potential risk factors or associations.

**Why the Correct Answer is Right**
Case-control studies are retrospective in nature because they involve looking back in time to identify cases and controls. This type of study design is useful for investigating rare outcomes or diseases, where a prospective study would be impractical or impossible. In a case-control study, the researcher starts with the outcome of interest and then looks back to identify potential risk factors or exposures. This retrospective approach allows researchers to examine the association between past exposures and outcomes.

**Why Each Wrong Option is Incorrect**
**Option A:** Prospective studies, on the other hand, involve following participants forward in time from exposure to outcome, which is not the case in a case-control study.

**Option C:** Cross-sectional studies involve examining a population at a single point in time and are not focused on identifying risk factors or associations between past exposures and outcomes.

**Option D:** While case-control studies are not prospective, cross-sectional, or both, the correct answer is not simply "none of the above," as it is a specific type of retrospective study.

**Clinical Pearl / High-Yield Fact**
When designing a case-control study, researchers must ensure that the selection of cases and controls is unbiased and that the study is free from confounding variables to produce accurate and reliable results.

**✓ Correct Answer: B. Retrospective**