People often say that a dog is man's best friend. Over thousands of years, man has taught his dogs to do many kinds of work besides guarding the home. For example, sheepdogs are famous for their ability to control a flock of hundreds of sheep.
Dogs have been used to aid disabled people for centuries. A guide dog can lead its blind owner. Nowadays, dogs can be taught to turn on light switches, open refrigerator doors and dial the telephone for their disabled owners. For the majority of people, however, dogs are simply pets and friends for both young and old members of the family.
人们总是说狗是人类最好的朋友。几千年来，除了看家外，人类还教会了狗去做许多其他的事，例如，牧羊犬就因其可以控制数百只羊的羊群而出名。
狗用来帮助残疾人已有好几个世纪了。导盲犬可以为盲主人引路。现在，人们还教狗为残疾主人打开电灯、开冰箱和拨电话。然而，对于大多数人来说，狗只是家里老人和孩子们的宠物和朋友。