问题 单项选择题

滤线栅是由许多薄的铅条和易透过X线的低密度物质作为充填物,交替排列组成的。在X线摄影中使X线的中心线对准滤线栅板中心,原射线投射方向与滤线栅的铅条排列间隙在同一方向上,能通过铅条间隙而到达胶片产生影像。由于被照体产生的散射线是多中心、多方向的,其中大部分散射线被铅条所吸收,只有一小部分通过。滤线栅的指标:
(1)栅比(R):滤线栅铅条高度与填充物幅度的比值为栅比。
(2)栅密度(n):n表示在滤线栅表面上单位距离(1cm)内,铅条与其间距形成的线对数,常用线/cm表示。

关于滤线栅的叙述正确的是

A.栅密度越大,消除散射线的能力越差

B.栅比越大,消除散射线的能力越差

C.栅比为铅条宽度与其高度之比

D.曝光量倍数越小越好

E.使摄影条件减小

答案

参考答案:D

解析:栅密度越大,栅比越大,消除散射线能力越强;栅比为栅条高度(h)与其栅条间隙的比值;使摄影条件加大。

阅读理解

阅读理解。

  Victor's hobby was collecting stamps. He had stamps from many countries, like England, Canada and

China. On his birthday, can you guess what people gave him? That's right---stamps.

  Victor's favourite stamps came from France. He had almost every stamp from 1954 to 2004. He

only needed one. That was a 1974 special edition. It was very hard to find.

  He looked for it everywhere. He asked his friends and relatives to help him.But nobody could find the

stamp. It made Victor very sad.

  "Don't worry. Never give up," his father said to him. "If you have enough patience, you'll find it one

day."

  "I hope so," Victor said.

  Victor also liked writing. He had a penfriend in France. They wrote to each other every month.

Victor's penfriend, Phillip, usually used new stamps to send letters. Sometimes, his mother gave him stamps

to use. Once Phillip's mother gave him a big, green stamp. It looked old. When Victor received the letter,

he

was very surprised. On the envelope, he looked carefully at the stamp. It was the 1974 special edition

stamp. Victor was so happy. He told his sister, his mother and his father. " You see," his father said. "You

did find your stamp. So, it's good to have two things in life."

  "What are they?" Victor asked.

  " Friends and patience." He answered.

1. It was very difficult for Victor to find a special French stamp of _____.

A. 1954      

B. 1974    

C. 1994            

D. 2004

2. What does the underlined word "patience" mean?

A. 勇气      

B. 知识        

C. 耐心            

D. 目标

3. Who owned the special edition stamp at the very beginning?

A. Phillip.    

B. Phillip's mother.    

C. Victor.  

D. Victor's father.

4. The passage mainly tells us that _____ is(are) important to people.

A. a happy family                      

B. a good hobby

C. relatives and friendship              

D. friends and patience

填空题