The correct response according to central place theory is: The threshold for a cardiology clinic is so high that it requires a larger range.
Central place theory suggests that specialized services, like those offered by cardiologists, require a larger population (or higher population density) to support their practice due to the higher demand for such specialized services. In contrast, general practice doctors have a lower threshold and can serve a wider range of patients, making them more common in various locations, including areas with lower population density.