Sam, a dog, was left behind in Colorado while his owners, Mr. And Mrs. Green moved to Southern California. They did not give the dog up. They found him a very nice home before they moved. They would have let Sam accompany them, but they were afraid the dog's presence would make it difficult for them to rent a house when they reached their _ . The Green family lived in Colorado for less than a year. Before that, they had lived in the same neighborhood in California to which they returned. So Sam had been there before, but only for a short time when he was young. Several months after the Greens left Colorado, after they were comfortably settled back in California, they heard a scratch at the door. They couldn't imagine who might be there. It never occurred to them that it might be Sam, because they were sure he was happily set up with his new family back in Colorado. When they opened the door, the Greens saw a dirty, tired dog with very hurting feet. The animal looked a little bit like Sam, but no one could believe that Sam could have walked 840 miles on his own. The tired dog spent the night under the family car. The next day, when he was more rested, he performed some of his old tricks. The Greens knew they had their own dog back. The story suggests that   _   .
dog owners have trouble renting many people treat their pets badly keeping a dog is easy dogs are too much trouble