Choose the best answer（根据短文内容，选择最恰当的答案）

All the people in Ben's family want to have a pet. Ben wants to have a dog. He says that a dog is a friend of men. But Ben's mother thinks that dogs need a lot of exercise. All the people in the family are very busy, so no one has time to help the dog take exercise. She wants to have a cat. She says that cats are clever and lovely （可爱的）. Ben's father wants to have some fish. He says that fish are clean and beautiful, and that they don't eat a lot. Ben's sister likes birds. She says that birds can sing beautifully. There is a pet shop near their home and there are many pets there. Tomorrow will be Sun-day. Ben and his family are going to buy some pets. What pets will they have? No one knows.