Public health official: Some researchers suspect that magnetic fields from high-voltage power lines can cause health problems for people who live especially near the lines. However, this is extremely unlikely: Beyond a distance of a few feet, the strength of the magnetic fields from high-voltage power lines is less than the average strength of magnetic fields in homes that are not located near such lines.

Which of the following would it be most useful to establish in order to evaluate the public health official's argument?

(A) Whether magnetic fields in homes that are not located near high-voltage power lines can cause health problems for the residents of those homes

(B) What proportion of people who live near high-voltage power lines believe that those lines may cause health problems

(C) Whether high-voltage power lines are routed near residential dwellings in urban areas

(D) What specific diseases or conditions are suspected by some researchers to result from exposure to magnetic fields from high-voltage power lines

(E) What is the average strength of magnetic fields in workplaces that are not located near high-voltage power lines