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一、有

Dogs can date back to the Stone Age. All dogs have the same ancestor. It is believed that their ancestor was much like a wolf. Other animals, such as the fox, came from this ancestor, too. Hundreds of thousands of years ago, man began to tame wild dogs. After the dogs were tamed, they were trained. The strong dogs became working animals. They were trained to pull heavy loads. They learned to keep an eye on the sheep and other animals. Working dogs had other jobs, too.

Some dogs were not strong. But they could help man hunt for game. Other dogs were best as pets.