If you read dog-training books or watch dog trainers on television, you've probably learned that to control your dog, you have to display dominance. It's commonly thought that because dogs are pack animals, they live according to dominance hierarchies(等级制度)---either you're the dominant top dog or you're a submissive(顺从的,降服的) underling(下属，部下，走卒). So, according to many popular dog-training methods, you've got to show a dog who's boss in order to make it sit, stay, fetch and obey other commands. But a study by researchers at the University of Pennsylvania suggests that using confrontational methods to train dogs often results in pets that are more aggressive and unmanageable(难以处理的,难管理的). Common techniques include hitting or kicking a dog, growling, rolling a dog on its back and holding it down, staring a dog down and grabbing a dog's jowls and shaking. The researchers' survey of 140 dog owners showed that these aggressive methods resulted in an aggressive response from dogs at least twenty-five percent of the time. So how should you train your dog? Many expert trainers advocate treating a dog much as you would a small child. Gentle training techniques emphasize(强调) building a healthy relationship with your dog by opening clear lines of communication and establishing a set of rules and boundaries(界限). This includes rewarding dogs for good behavior and not expecting your dog to obey all your commands right away. Like most kids and even many adults, learning to behave takes time and patience.