问题 单项选择题

关于继发性牙本质叙述正确的是( )

A.在前牙中,髓腔顶和底部的继发性牙本质比侧壁厚
B.继发性牙本质在各个部位分布均匀
C.也称反应性牙本质
D.牙本质在一生中仍可继续不断地形成,但形成速度减慢,这种后来形成的牙本质为继发性牙本质
E.以上均不对

答案

参考答案:D

解析: 继发性牙本质是牙本质在牙齿发育完成后,在一生中仍可继续不断地形成,但形成速度减慢,这种后来形成的牙本质为继发性牙本质。

阅读理解

阅读理解.

                                                             A Trip to the Forest

    One day Bob took two of his friends into the mountains. They put up their tents and then rode off to

a forest to see how the trees were growing. 

    In the afternoon when they were about ten kilometres from their camp (营地), it started to snow.

More and more snow fell. Soon Bob could hardly see his hands before his face. He could not find the

road. Bob knew there were two roads. One road went to the camp, and the other went to his house.

But all was white snow. Everything was the same. How could he take his friends back to the camp?

    Bob had an idea. The horses! Let the horses take them back! But what would happen if the horses

took the road to his house? That would be a trip of thirty-five killometres in such cold weather!

    It was getting late. They rode on and on. At last the horses stopped. Where were they?  

None of them could tell. John looked around. What was that under the tree? It was one of their tents!

1. John and his two friends went to the forest to ________.

    A. build their camp

    B. find their way home

    C. enjoy the mountains in the snow

    D. watch the trees in the forest

2. They could not find their way back because ________.

    A. there was only one road to their camp

    B. they couldn't decide which of the two roads led to their tents

    C. there were no roads in the mountains at all

    D. everything was covered by the white snow

3. It is clear that they wanted the horses to take them to _______.

    A. John's house

    B. the camp

    C. the forest

    D. the mountains

4. The horses stopped because _______.

    A. it was getting late

    B. they were tired after running for a long way

    C. they knew that they had got to the camp

    D. they had seen John's house

5. The story happened _______.

    A. on a cold winter day

    B. on a dark snowy evening

    C. in a cold camp far from villages

    D. at night when nothing could be seen

填空题