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问题 单项选择题

食管癌前后对穿野一般照射野宽度为

A、4C、M 

B、4.5C、M 

C、5C、M 

D、5.5C、M 

E、6C、M

答案

参考答案：E

单项选择题

下列关于眼睛和眼镜的说法中不正确的是（）。

A.人的眼睛相当于凸透镜

B.近视眼的折光能力太强

C.近视眼看远处的物体不清晰

D.近视眼镜镜片就是凸透镜
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问答题

In the figure above, two searchlights S1 and S2 are located 10,000 feet apart, each covers an area of radius 10,000 feet, and each is located 8,000 feet from the railroad track. To the nearest 1,000 feet, what is the total length x of track spanned by the searchlights ？
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