题目

  Today, there are more than 100 kinds of dogs in the world. Many people like to have dogs as their pets. Dogs are friends of man because they are lovely and they are faithful to their masters.   Dogs can do a lot of work for man. They play with us. They hunt with us. They also keep door for us. But long ago, dogs all over the world were wild(野生的).   All dogs have the same ancestor. People believe that a dog’s ancestor may be a wolf. Other animals, such as the fox, came from this ancestor, too. Millions of years ago, man began to feed and train wild dogs. The strong dogs bec 下图是某物体运动的v－t图像，则图ABCD中能相应表示出该物体运动的s－t图像的是 [　　] A． B． C． D．