某班学生为探究绿色植物的光合作用，设计如下实验装置甲、乙、丙，请据图作答：

   To be a good teacher, you need some of the gifts of a good actor; you must be able to hold the attention and interest of your audience; you must be a clear speaker, with a good, strong, pleasant voice which is fully under your control; and you must be able to act what you are teaching, in order to make its meaning clear.
   Watch a good teacher, and you will see that he doesn't sit still before his class; he stands the whole time he is teaching; he walks about, using his arms, hands and fingers to help him in his explanations, and his face to express feelings.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, even his movements and the ways in which he uses his voice are usually fixed beforehand(预先).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. His audience take an active part in his play: they ask and answer questions, they obey orders, and if they don’t understand anything, they say so. The teacher can't learn his part by heart, but must invent it as he goes along.
   I have known many teachers who are fine actors in class but are unable to take part in a stage-play because they can't keep strictly to what another has written.

阅读下文，回答相关问题
        北国风光，千里冰封，万里雪飘。望长城内外，惟余莽莽；大河上下，顿失滔滔 山舞银蛇，原驰蜡象，欲与天公试比高。须晴日，看红装素裹，分外妖娆。
        江山如此多娇，引无数英雄竞折腰。惜秦皇汉武，略输文采；唐宗宋祖，稍逊风骚；一代天骄，成吉思汗，只识弯弓射大雕。俱往矣，数风流人物，还看今朝。