Radioactive radon gas emanating from rock such as granite puts inhabitants of houses built on such rock at greater risk of lung cancer the longer the inhabitants are exposed. Protective steps should be taken if radon measurements exceed 4 picocuries per liter; this recommendation is based on 70 years of occupancy by any one person.
If a 65-year-old homeowner concludes from the information above that radon testing for the new home she has purchased will not be necessary, then each of the following, if true, weakens the homeowner’s argument EXCEPT:
A．Houses in which the homeowner previously lived were in an area where elevated radon levels have been found.
B．Houses near the homeowner’s new home have radon levels much higher than the 4 picocuries per liter threshold, levels that require immediate action to reduce exposure to any occupants.
C．The homeowner’s granddaughter, who is eventually to inherit the new house, now lives there with her children.
D．The homeowner smokes cigarettes, and smoking increases the radon-exposure risks over those given in the information.
E．(E) The strata underlying the homeowner’s new home are known to be of rock different from the kinds from which radon emanates.
