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(忠诚的) 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（祖先）．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 下列哪组食物不需消化就能被消化道内壁所吸收（ ）A．糖类B．脂肪C．蛋白质D．维生素