（1）Many people walk with their dogs along the street in Shanghai.
（2）The dog is the most useful animal in the world.
（3）People used to keep dogs as friends because they lived in lonely places.
（4）For a child，a dog can be his guard（守卫） because it can keep him safe.
（5）For young people，a dog can be their friend when they feel lonely at home.
（6）For old people，a dog can be their child when their real children have grown up and have their own home.