Answer: Option (C) is correct.
Step-by-step explanation:
Observational studies are referred to as the ones where researchers or individuals examine the result of a risk factor, symptomatic test, or several other interventions without appealing to alter who is/isn't bared to it. There are two types of observational studies, these are cohort and case-control studies.
Therefore from the above stated, we can further conclude that the given statements are an example of an observational study.