单选题 .  To be a good teacher, you need some of the gifts of a good actor: you must be able to     21    the attention and interest of your students; you must be a     22    speaker, with a good, strong,     23    voice which is fully under your control; and you must be able to     24    what you are teaching in order to make its meaning clear.     25    a good teacher and you will see that he does not sit still     26    his class; he stands the whole time when he is teaching; he walks about, using his     27    , hands and fingers to help him in his explanations, and his face to express feelings. Listen to him, and you will     28    the loudness, the quality and the musical note of his voice always     29    according to what he is     30    about.
    The fact that a good teacher has some of the gifts of a good actor doesn't     31    that he will indeed be able to act     32    on the stage, for there are very important     33    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     34    words each time he plays a certain part;     35    his movements and the ways in which he uses his voice are usually     36    beforehand. What he has to do is to make all these carefully learnt words and actions seem     37    on the stage.
    A good teacher     38    in quite a different way. His students take an active part in his     39    ; they ask and answer questions; they obey orders; and if they don't understand something, they will say no. The teacher therefore has to suit his act to the needs of his students. He cannot learn his part by heart, but must     40    it as he goes along.21.