问题 单项选择题

500mAFSK302-1A到程控X线机,当发现副床小焦点摄影管电流的实际值与设定不一致时,需调节灯丝板上相应的电位器,即通过改变灯丝加热电压波形的什么来进行微调()

A.频率

B.脉宽

C.频率和脉宽同时改变

D.幅值

E.以上方法都可以

答案

参考答案:B

阅读理解

阅读理解

                                     Moving out, moving back

       In the countries all over the world, people are leaving the countryside in large numbers to find jobs in

the cities. They leave because the countryside is much poorer than the city, and often there isn't much work there. Services such as hospital and transport are usually much better in cities than they are in the country. They hope that their lives will improve when they move to the city.

       But in the big cities of Europe and America-London, Paris, New York, people are moving out of

the city. These are usually families who have some money, and want to live a quieter life. They are tired of

the noise and the dirt of the city, tired of the crowded streets, crowded trains and buses. They don't want

to sit in traffic any more. They want a house with a garden, and clean air that isn't polluted.

       So they move out. Some don't go very far, just a little way out of the city, to the towns near the cities, other people move to the real countryside with sheep and cows and green fields!

       There, they start new lives and try to make new friends.

       Not all those who move from the city to the countryside are happy. After two or three years, many

people who have done this feel that it was a big mistake. They don't make so much money and there isn't much to do. Country people are very different and aren't always very friendly.

       As a result, quite a lot of people who have moved to the countryside move back to the city. "It's

wonderful to see crowded in the streets and cinema lights," they say, "I'm so glad back in the city !"

1. Is there often much work to do in the countryside?

                                                                                   

2. What kind of families are moving out of the city?

                                                                                   

3. What are they tired of about the city? (答两点即可)

                                                                                    

4. What do they think of the people in the countryside?

                                                                                    

5. What can we learn from the sentences "It's wonderful to see crowded in the streets and cinema lights" ?

                                                                                    

单项选择题