A.ntists always ask questions when it is impossible for you to answer.One day ,my dentist had just pulled out one of my teeth and asked me to sit in a chair to rest for a while. I tried to say something ,but my mouth was full of cotton-wool(药棉). He knew I collected stamps and asked me whether I got any new recently. He then asked me how my brother was and whether I liked my new job. B.I could not speak ,l either nodded or made strange noises to answer these questions. At the same time ,l tr;ed hard to use my tonguec舌头) to find the hole(洞) in the place of my bad tooth. Suddenly I felt very worried because the bad tooth was still there ,but I could not say any- thing. At last the dentist pulled the cotton-wool out of my mouth ,and I was able to tell lum that he had pulled out the wrong tooth. C.)21. Why did the dentist ask me to rest for a while? D.I felt tired. E.I felt painful.