The extremely high incidence of birth defects and cancer among children in Tellersville, Nevada, has long been suspected to be linked to the nuclear-weapons facility in which nearly three-quarters of the town's population works. It now appears, however, that the town's water supply, tainted by the discharges of a nearby plastics factory, is to blame for the town's health problems. Scientists have studied two groups of rodents. One group was exposed to the same level of radiation present at the nuclear-weapons facility but given pure water. The other was exposed to no radiation but given tainted water from Tellersville. The latter group showed an incidence of cancer and birth defects ten times higher than normal and six times higher than that of the pure water group.

Which one of the following, if true, most undermines the conclusion that Tellersville's water supply is responsible for the town's health problems?


A) Nuclear radiation is not a cause of birth defects and cancer among humans.

B) While radiation tends to affect all mammals in similar ways, the toxins present in Tellersville's water supply have very different effects on rodents or other mammals.

C) Water from a new source would help Tellersville prevent future health risks.

D) Long-term exposure to toxins in the water supply in combination with exposure to radiation may significantly increase the incidence of birth defects and cancer among children.

E) Certain toxins in the water supply of Tellersville are likely to have served to protect those drinking it from some of the harmful effects of radiation.


I believe the answer is either D or B. Option B does not exactly clarify whether the effects will be less severe or more severe in mammals. Since pure water group also shows higher incidence, it could be that both the factors are responsible and not the water supply alone. The pure water-radiation shows higher incidence, so radiation factor cannot be ruled out. So answer should be D.

Can any expert clarify on this.