Critical Reasoning

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.

IMO B
Scope Shift. Problems in children but tested on rodents.
B) toxins have different effect on rodents and children. Thus if water supply affects rodents, we can't say it affects children also.

A) Nuclear radiation is not a cause of birth defects and cancer among humans.- OUT. Strengthens the argument

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.- CORRECT. Scope shift. The author talks about rodents and is assuming that the effects seen on rodents are similar to those on humans. This option attacks this assumption and says well, the effects are different.

C) Water from a new source would help Tellersville prevent future health risks. - OUT - Irrelevant. How does it answer the question whether contaminated water is the cause of cancer effects on humans ??

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. - OUT - The argument says that town's water supply is to be blamed for the health problems of the town. This option says that water ssupply in COMBINATION WITH radiation is responsible for the health effects. We don't know whether it's the water which is causing health hazards or the radiation !! Does not weaken ..

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. - OUT. . Ok. Certain TOXINS protect against some of the effects caused by radiation. But what about other harmful effects of radiation?? It serves no protection against other effects of radiation. so who to blame- the radiations or the water itself ?? Dont know !! It could be anything.. This does not weaken the claim that it is the water that has to be bamed.

IMOB. OA Pls.

IMO: B

The stem deals with children, while the conclusion is based on the studies conducted on rodents.

OA pls!

IMO B

OA is B.