当别人对你说“Thank you.”时，你应该回答：(    )

在  ${\left(\sqrt{x}+\frac{2}{x}\right)}^n$的二项式展开式中，只有第5项的二项式系数最大，则 n= （  ）

生物圈中生物所需的能量最终来自（　　）

从正面观察如图的两个物体，看到的是（　　）

   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