问题
单项选择题
采用电磁技术方式展宽电子束的优点是（）。
A.可以降低医用直线加速器机头的重量
B.使出射电子束的能谱分布窄，且可降低X线污染
C.和使用散射箔方式的效果一样
D.可以获得高能电子束
E.便于在使用中的电子束能量间切换
答案
参考答案：B
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采用电磁技术方式展宽电子束的优点是（）。
A.可以降低医用直线加速器机头的重量
B.使出射电子束的能谱分布窄，且可降低X线污染
C.和使用散射箔方式的效果一样
D.可以获得高能电子束
E.便于在使用中的电子束能量间切换
参考答案：B
| 完形填空。 |
| Lily is a little girl. She is not ① . She ② how to read or write. But her sister Jill is ③ . She is ten years old. She knows how to read and write. One day, Jill ④ her little sister in the room. She looks ⑤ the table. There ⑥ a pencil in ⑦ hand. She is writing. "What are you writing, Lily?" she asks. "I'm writing ⑧ my friend Rose. " " ⑨ how can you? You don't know how to write," says her sister. "Well," says Lily, "It doesn't matter. Rose doesn't know how to ⑩ , either. " |
| （ ）①A. at school （ ）②A. doesn't know （ ）③A. school girl （ ）④A. write （ ）⑤A. or （ ）⑥A. how （ ）⑦A. my （ ）⑧A. from （ ）⑨A. Or （ ）⑩A. dance | B. work B. know B. school girls B. reading B. under B. is B. their B. to B. So B. sing | C. study C. don't know C. boy student C. seeing C. at C. are C. his C. for C. But C. write | D. a student D. doesn't knows D. student girl D. sees D. in D. have D. her D. with D. And D. read |