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

①L期有 8 条染色体

②P期紧接在L期之后

③P期与M期细胞内核DNA数相等

④P期有8条染色单体

A

    Most Americans start to school at the age of five when they enter kindergarten(幼儿园). Children do not really study at this time. They only attend for half the day and learn what school is like. Children attend elementary school for the next six years. They learn to read and write and work with numbers. They also study the world and its people. After they leave elementary school, children go to junior high school for three years and senior high school for another three years. This is called secondary education. In some places, the children go to elementary school for eight years and high school for four. In all, elementary and secondary education together take twelve years to complete excluding （不包括）kindergarten.

根据短文，选择最恰当的选项。