A

Before， I thought that a man who was wise and good would become rich， but now I know this is not always true． I learned it from my teacher． He is both wise and good， but he is not rich at all． He may become rich if he gives up(放弃) teaching and goes into business．  But he likes his job and thinks it，s wonderful to help young people． He stays at school from morning till night and works very hard． He always smiles at us when we go to ask him for help． He is kinder to us than any other teacher in our school． I think it must be easier to learn history or math than to learn how to become a man like him． He scolds(责备 ) us when we do something wrong，but it makes us try to do better．We all wish to study with him as long as possible． But that may be impossible． Some of us may become doctors， some become businessmen， some be- come engineers， some become writers， but we all want one thing very much． It is that we all want to be teachers in the future．

(      )21． The writer thinks his teacher is_________．