Dear Pet,
   Without knowing more about you, it's hard for me to give you some good advice.
   But first, I am sure that you are1 . You said that nobody would care if you left home. What about your2?  And other family members? It seems that you are very3 . You'd better go to a doctor or talk 4 your parents. They will be able to help you.
Second, I'm sure there’s someone else in your class who feels lonely, 5. You never know6other people feel. Try to make friends with your classmates. And you could7a club to meet new people and make friends, too.
   You8find happiness in yourself. So my9advice is to write a list of all the good things about yourself, learn to like yourself, and then10 will see your confidence (信心)and like you, too.
                                                                                                                                                                                  Editor

哺乳动物之所以是动物中最高等的类群，是因为哺乳动物具有一系列高等特征，能适应各种复杂多变的环境，据此请回答下列问题：