Jeff: Proposed regulations concerning the use of animals in scientific experimentation would prohibit experimentation on those species that humans empathize with: dogs and horses, for example. But extensive neurological research on mammals shows that they are all capable of feeling pain, just as dogs and horses are. Hence, this proposal should be extended to all experimentation on all mammals. Miranda: Yet the issue of pain is not the crux of the matter. Experimentation on any nonhuman animal undermines respect for life itself because only humans are capable of consenting to an experiment. Since any activity that undermines respect for life diminishes the quality of all of our lives, the new regulations should ban all such experimentation. Which one of the following is a principle that, if established, would best support Jeff's conclusion? ['Scientific experimentation should be prohibited on any creature that is capable of feeling pain.', 'Only those experiments on animals that are known to cause those animals pain should be prohibited.', 'Regulations on the use of animals in scientific experimentation should be primarily concerned with respecting the feelings of the humans who will perform those experiments.', 'Whatever means are used to determine whether dogs and horses feel pain should also be used to determine whether other animals feel pain.']