Answer: D). This was a cross-sectional cohort study
Step-by-step explanation:
The given situation is an example of cross sectional cohort study because the investigator choose the samples from the population using cross sectional method and use the same sample source for analyzing the independent variables for specific period of time or intervals of time to assess the history of exposures and outcomes.
Here, the lung function is tested at an interval of 7 years compared with the levels of exposure to the coal ash so it is the example of cross sectional cohort study.
They will earn $50 within ten years because the 5% gives five dollars a year for 10 years
