听力原文： Is your family interested in buying a dog? A dog can be a happy addition to your family, but if you choose the wrong kind of dog, the consequences can cause you a lot of trouble. Families should sit down and thoroughly discuss the problems involved before buying a dog. Even if the children in your family are the ones who want the dogs, the parents are the ones who are really responsible for seeing that the animal is properly cared for. If you dont know much about dogs, its a good idea to go to the library or the ASPCA for books about various kinds of dogs, as well as books about how to train a puppy. When a book describes a dog as an ideal hunting dog, it probably means that the dog wont be happy living in a small apartment. Dog breeds vary in popularity as the years go by. One of the most popular dogs these days is the German shepherd. This is because it provides protection as well as companionship. The family should be warned that these dogs grow up to be very big, and may be too powerful for children to handle. If space is limited, a toy dog may be a good choice. These dogs are very small and easy to train. They dont need to be walked daily, since they can exercise in the space available in the home. Questions 16 to 18 are based on the passage you have just heard. 16. What is the passage mainly about? 17. How does the speaker suggest people get information about dogs? 18. Why is the German shepherd a popular dog according to the passage?16．