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My uncle, Mr. Smith is a farmer. He grows much rice and he feeds many pigs, chicks and ducks. He is always happy. He has two brown dogs. One is big and the other is small. He likes them very much.

One day, my uncle's friend comes to visit him. When the friend sees the holes in the door, a large hole and a small hole. He is surprised and says，"My dear friend, why are there two holes in your door?”

"Let my dogs come in and come out, of course." my uncle answers.

The friend asks, "But why are there two holes? One is enough!"

"But how can the big dog go through the small hole?" my uncle says.