**Core Concept**
A prevalence study is a type of epidemiological study that aims to measure the total number of cases of a disease or condition present in a population at a specific point in time or over a specified period.

**Why the Correct Answer is Right**
Prevalence studies are also known as prevalence surveys or cross-sectional studies, as they involve collecting data from a sample of the population at a single point in time. This type of study is useful for understanding the burden of disease, identifying risk factors, and planning healthcare resources. Prevalence studies can be conducted in various settings, including communities, hospitals, or clinics.

**Why Each Wrong Option is Incorrect**
**Option A:** Incidence study - This type of study measures the number of new cases of a disease or condition that occur over a specified period, rather than the total number of cases present at a single point in time.

**Option B:** Cohort study - This type of study involves following a group of individuals over time to examine the development of a disease or condition, but it does not aim to measure the total number of cases present at a single point in time.

**Option C:** Case-control study - This type of study involves comparing individuals with a specific disease or condition (cases) to those without the disease or condition (controls), but it does not aim to measure the total number of cases present at a single point in time.

**Clinical Pearl / High-Yield Fact**
Remember that prevalence studies are useful for understanding the burden of disease and planning healthcare resources, but they have limitations, such as not being able to establish causality or temporal relationships between risk factors and disease.

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