Dogs like living with people. They are very friendly. They can do many things for people.   Some dogs help people to look after sheep, other dogs help them to find the lost children.① And some of the dogs can help the blind.(盲人)

   There is a kind of dog whose name is Seeing Eye Dog②. Now we can see this kind of dog all over the world. They are working for the blind. The Seeing Eye Dog is strong and easy to train(训练). He helps the blind to walk from place to place. Before a dog becomes a Seeing Eye Dog, he must be in a training school for about three months. First the dog has to learn to sit or stay when he hears the trainer's call. In his next lesson the dog learns to take his trainer across busy streets ③. The dog has many things to learn. 在……的末尾④the training, he must take tests. When he passes the tests, the Seeing Eye Dog will do things by himself.   Now he can help the blind people. The new master(主人) may be a man , a woman or even a child. It takes the dog and his blind master about a month learning to work and live together.⑤

唐初，以三省长官为宰相。从贞观年间开始，皇帝开始任命中央其他官员为相。这些非三省长官的宰相有各种名义，如参知机务、参预朝政、同中书门下平章事等。这样做的目的是（    ）