III．阅读理解． (20分)
A
Dentists 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．
As 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．
( )21． Why did the dentist ask me to rest for a while?
A． I felt tired．
B． I felt painful．
C． I just had a tooth pulled out．