Answer:
B. A cross-sectional study.
Step-by-step explanation:
Observational studies include the observation of the effects of risk factors, diagnostic examinations, treatment or other intervention by the researchers in order to measure certain outcomes.
A cross-sectional study also known as transverse study or prevalence study is a sub-branch of observational study that involves the analysis of data(cross-sectional data) from the population or a representative subset at a precise point of time. Thus, the problem statement provided here illustrates the cross-sectional study as it observes and analyzes cross-sectional data.