**Core Concept**
Hepatitis B is a major global health concern, causing acute and chronic liver disease. Epidemiologic studies of Hepatitis B aim to understand its transmission dynamics, risk factors, and disease burden.

**Why the Correct Answer is Right**
The correct answer is based on the understanding that Hepatitis B is primarily transmitted through bodily fluids, including blood, semen, and other bodily secretions. Serologic markers, such as the Hepatitis B surface antigen (HBsAg), are essential for identifying infected individuals and understanding the epidemiology of the disease. The correct answer is **Case-Control Study**, as it is an observational study design that compares individuals with a specific outcome (e.g., Hepatitis B infection) to those without the outcome, allowing researchers to identify risk factors and associations.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the epidemiologic study of Hepatitis B.
**Option B:** While cohort studies can provide valuable information on disease transmission, they are not the most effective design for studying the epidemiology of Hepatitis B.
**Option C:** Cross-sectional studies can provide a snapshot of disease prevalence, but they are not ideal for understanding the temporal relationships between risk factors and disease outcomes.

**Clinical Pearl / High-Yield Fact**
Remember that Hepatitis B is a leading cause of chronic liver disease worldwide, and understanding its epidemiology is crucial for developing effective prevention and control strategies.

**Correct Answer:** C. Cross-sectional studies.