A、The teacher must learn everything by heart. B、He knows to control his voice better than an actor. C、He has to deal with unexpe

[29] To be a good teacher, you need some of the gifts of a good actor -- the key point is that you must know how to hold the attention and interest of your audience. Watch a good teacher, and you will see that he does not sit motionless before his class: he stands the whole time while teaching; he walks about, using his arms, hands and fingers to help him in his explanations, and his face to express feelings.
    Listen to him, and you will hear the loudness, the quality and the musical note of his voice always changing according to what he is talking about. [29] However, all this doesn’t mean that he will indeed be able to act well on the stage, for there are very important differences between the teacher’s work and the actor’s. The actor has to speak words which he has learnt by heart; he has to repeat exactly the same words each time he plays a certain part. What he has to do is to make all these carefully learnt words and actions seem natural on the stage. A good teacher works in quite a different way. [31] His audience takes an active part in his play; they ask and answer questions, they obey orders, and if they don’t Understand something, they say so. [30] The teacher therefore has to suit his act to the need of his audience, which is his class. He cannot learn his part by heart, but must invent it as he goes along.