pets are loved by people. they not only are good friends to their masters but also become members of the family. although they are not human beings, their behavior sometimes is better than the human beings, for they always remain obedient and loyal to the master. there are many stories in which we are told that a pet saved his or her master's life or even traveled thousands of miles to return home. this makes them more lovely. moreover, trained pets are very helpful. for instance, a trained dog can help the blind to walk and a trained pig can even find out drugs from the imports goods.

　　but pets are sometimes trouble-makers. some pets such as dogs or snakes may attack people unexpectedly. a lot of people become ill or get infected because of the virus carried hy their pets. and some pets are dirty and poisonous. therefore, we do not advocate keeping pets.