3.A foreign language teacher has to not only make his students understand the language,namely the pronunciation,vocabulary,grammar,etc.,he must also develop their communicative competence so that they can use the language they have learned correctly,appropriately and expressively in real situations.In order to do well this complicated job,the teacher needs to know,apart from a comprehensive knowledge of the language and the ability to use it,as many teaching methods and techniques as possible,and understand the underlying theories and principles,therefore he not only knows what to teach and how to do it,but also why he should do it in a certain way and how to solve problems when they arise.In this way he will have full confidence in doing his job well.