Question ID:PT71 S1 Q13 Passage:Animal feed should not include genetically modified plants. A study found that laboratory rats fed genetically modified potatoes for 30 days tended to develop intestinal deformities and a weakened immune system, whereas rats fed a normal diet of foods that were not genetically modified did not develop these problems. Stem:Which one of the following, if true, most weakens the argument? Correct Answer Choice:AChoice A:Potatoes are not normally a part of the diet of laboratory rats. Choice B:The rats tended to eat more of the genetically modified potatoes at the beginning of the 30 days than they did toward the end of the 30 days. Choice C:Intestinal deformities at birth are not uncommon among rats bred in laboratory conditions. Choice D:Genetically modified potatoes have the same nutritional value to rats as do potatoes that are not genetically modified. Choice E:The researchers conducting the study were unable to explain how the genetic modifications of the potatoes would have caused the intestinal deformities or a weakened immune system in the rats.