A research project tracking residents over a ten-year period is an example of which type of study?

The correct answer is C. Longitudinal. A longitudinal study is characterized by the observation of the same subjects over a period of time. In this case, tracking residents over a ten-year period means that the research is collecting data at multiple time points from the same individuals. This allows researchers to observe changes, trends, and long-term outcomes within the same population, providing valuable insights that are not possible with other study designs.

In contrast, concurrent studies typically involve data collection at a single point in time or over a shorter timeframe without the extended follow-up characteristic of longitudinal studies. Cross-sectional studies assess a population at one specific moment, offering a 'snapshot' rather than a dynamic view over time, which would not allow for tracking changes in the same residents. Retrospective studies, on the other hand, analyze data collected from past events regarding subjects, often through existing records. However, since the question specifies that the residents are tracked over ten years into the future, this description aligns precisely with the characteristics of a longitudinal study.