Many of those who are most opposed to cruelty to animals in the laboratory, in the slaughterhouse, or on the farm are people who truly love animals and who keep pets. The vast majority of domestic pets, however, are dogs and cats, and both of these species are usually fed meat. Ttherefore, many of those who are most opposed to cruelty to animals do, in fact, contribute to such cruelty. Which one of the following is an assumption made by the argument? ['Many popular pets are not usually fed meat.', 'Feeding meat to pets contributes to cruelty to animals.', 'Loving pets requires loving all forms of animal life.', 'Many of those who are opposed to keeping dogs and cats as pets are also opposed to cruelty to animals.']