根管机械预备的目的如下，除外（）
A.清除主根管内感染
B.清除根管壁的感染
C.扩大根尖孔以利引流
D.减少弯曲根管的弯曲度
E.预备根管形态以利充填
参考答案：C
解析：根管机械预备的目的，完善清洁根管系统的所有部分（清除主根管内感染，清除根管壁的感染），形成根尖孔至根管口的连续锥形的管形结构（减少弯曲根管的弯曲度，预备根管形态以利充填），预备后保持根管的原始形态，形成根充挡，适应根管自然弯曲，避免过度预备，由此可见A、B、D、E不选。为了防止细菌和根管内容物推出根尖孔外，要在根尖孔形成根充挡，不可扩大根尖孔，所以此题选C。
| 阅读理解。 |
| Mr and Mrs Smith had always spent their summer holidays in New Jersey (新泽西) in the past, staying in a small inn (旅店) at the foot of a hill. One year, however, Mr Smith made a lot of money in his business, so they decided to go to London and stay at a really good hotel while they went touring around that famous city. They flew to London and arrived at their hotel late one evening. They had expected that they would have to go to bed hungry, because in that small inn in New Jersey, no meals were served after seven. They were surprised when the waiter asked whether they would take dinner there that night. "Are you still serving dinner?" asked Mr Smith. "Yes, certainly, sir," answered the waiter. "We serve it until half past nine." "What are the times of meals then?" asked Mr Smith. "Well, sir," answered the waiter. "We serve breakfast from seven to half past eleven in the morning, lunch from twelve to three in the afternoon, tea from four to five, and dinner from six to half past nine." "But that hardly leaves any time for us to see the sights of London." said Mr Smith. |
| 1. Mr and Mrs Smith had always spent their holidays in ______. |
[ ] |
| A. New York B. London C. New Jersey D. Washington |
| 2. When Mr and Mrs Smith had a lot of money, they decided to go to ______. |
[ ] |
| A. their hometown B. the capital of England C. New Jersey D. a small city in England |
| 3. They went to London by ______. |
[ ] |
| A. sea B. plane C. train D. bus |
| 4. From the story we know that this was the ______ time for Mr and Mrs Smith to go to London. |
[ ] |
| A. first B. second C. third D. fourth |
| 5. What does the sentence "But that hardly leaves any time for us to see the sights of London" mean? |
[ ] |
| A. We can go to see the sights of London at any time. B. We have enough time to see the sights of London. C. We can see more sights of London. D. We have little time to see the sights of London. |