What is the correct condition under which long-term tests are conducted?

Long-term radon tests are designed to measure the concentration of radon gas over an extended period, typically 90 days to a year. Conducting these tests under normal living conditions is crucial because it allows for an accurate assessment of radon levels that occupants would typically experience. This includes regular ventilation patterns, typical occupancy levels, and standard household activities that can influence indoor air quality.

By maintaining normal living conditions, the test results reflect real-world exposure levels rather than artificially manipulated environments that might not occur in everyday life. This approach ensures that homeowners receive reliable data that they can use to make informed decisions about radon mitigation if necessary.

Other options suggest scenarios that would not yield representative measurements of radon exposure. For instance, having the house empty or requiring extreme weather conditions would not provide a valid picture of typical indoor radon levels. Similarly, leaving all windows open could drastically alter indoor air patterns, skewing the results and making them less reflective of the actual risks faced by residents.