有效射线束宽度与哪个系统参数无关 A．焦点尺寸 B．探测器孔径_爱下问搜题

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问题单项选择题

有效射线束宽度与哪个系统参数无关

A．焦点尺寸
B．探测器孔径
C．一次投影射线束通过的路径
D．焦点至受检者的距离
E．焦外辐射至探测器的距离

答案

参考答案：D

解析：在扫描野中心射线束的宽度，又被称为有效射线束宽度，与五个系统参数密切相关，它们是焦点尺寸、探测器孔径、一次投影射线束通过的路径、焦点至探测器的距离和焦外辐射至探测器距离的比值。

完形填空

When I was in seventh grade, I volunteered at a local hospital during the summer. I spent most of the time there with Mr. Gillespie. He never had any      , and nobody seemed to care about his condition. I spent many days there       his hand and talking to him, helping with anything that needed to be done. He became a close friend of mine,       Mr. Gillespie was in a coma (昏迷).
I left for a week, and when I came back, Mr. Gillespie was      . I didn't have the courage to ask any of the nurses where he was, for       they might tell me he had died.
So with many questions      , I continued to volunteer there.
Several years later, I was at a gas station when I noticed a       face. When I realized who it was, my eyes filled with tears. He was alive? I got up the       to ask him if his name was Mr. Gillespie, and if he had been in a       about 5 years ago. With an uncertain look on his face, he       yes. I explained how I knew him. His eyes were       with tears, and he gave me the warmest hug.
He began to tell me when he       there comatose (昏迷的), he could hear me talking to him and could       me holding his hand the whole time. He thought it was an      , not a person, who was there with him. Mr. Gillespie firmly believed that it was my       and touch that had kept him alive.
Then he told me about his life and what happened       him to put him in the coma. We both cried for a while, said our goodbyes and       our separate ways.
Although I have not seen him since then, he fills my heart with joy every day. I know that I made a       between his life and his death. More      , he has made a very big difference in my life, too. I will never forget him and what he       for me: he made me an angel.

C．convenience

C．conversation

C．interviewee

A．importantly

单项选择题

锥体系统是指

A．上运动神经元

B．下运动神经元

C．小脑皮层细胞

D．脊髓巨角细胞

E．上及下运动神经元