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问题 单项选择题

按照射野平坦度的定义，射野内一定范围中最大剂量点与最小剂量点剂量值之差与其两者的平均值之比，称为该射野的平坦度。该范围是指（）。

A.依照射野的几何大小，由射野边缘向射野中心等比地缩小为原野大小的50%

B.依照射野的几何大小，由射野边缘向射野中心等比地缩小为原野大小的80%

C.依照射野的几何大小，由射野边缘向射野中心等比地缩小为原野大小的90%

D.依照射野的几何大小，由射野边缘向射野中心等比地缩小为原野大小的60%

E.依照射野的几何大小，由射野边缘向射野中心等比地缩小为原野大小的20%

答案

参考答案：B

材料题

造纸术是我国古代的四大发明之一。

结合所学知识，回答下列问题。

（1）造纸术发明前，人们的书写材料是什么？

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（2）西汉时期的造纸技术如何？

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（3）“蔡侯纸”是谁制造的？他是什么时代的人？

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（4）“蔡侯纸”的特点是什么？

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（5）造纸术的发明与传播，有什么世界意义？

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单项选择题

Mr. Peter Johnson, aged twenty-three, battled for half an hour to escape from his trapped car yesterday when it landed upside down in three feet of water. Mr. Johnson took the only escape route—through the boot.
Mr. Johnson’s car had finished up in a ditch at Romney Marsin, Kent after skidding on ice and hitting a bank. "Fortunately, the water began to come in only slowly, " Mr. Johnson said. "I couldn’t force the doors because they were jammed against the walls of the ditch and dared not open the windows because I knew water would come flooding in. "
Mr. Johnson, a sweet salesman of Sitting Home, Kent, first tried to attract the attention of other motorists by sounding the horn and hammering on the roof and boot. Then he began his struggle to escape.
Later he said, "It was really a half penny that saved my life. It was the only coin I had in my pocket and I used it to unscrew the back seat to get into the boot. I hammered desperately with a hammer trying to make someone hear, but no help came. "
It took ten minutes to unscrew the seat, and a further five minutes to clear the sweet samples from the boot. Then Mr. Johnson found a wrench and began to work on the boot lock. Fifteen minutes passed by. "It was the only chance I had. Finally it gave, but as soon as I moved the boot lid, the water and mud poured in. I forced the lid down into the mud and scrambled clear as the car filled up. "
His hands and arms cut and bruised, Mr. Johnson got to Beckett Farm nearby, where he was looked after by the farmer’s wife, Mrs. Lucy Bates. Huddled in a blanket, he said, "That thirty minutes seemed like hours. " Only the tips of the car wheels were visible, police said last night. The vehicle had sunk into two feet of mud at the bottom of the ditch.

Which of the following objects is the most important to Mr. Johnson

A. The hammer.
B. The coin.
C. The screw.
D. The horn.
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