问题
单项选择题
乳腺摄影主要利用X线的（）。
A.生物效应
B.光电效应
C.散射效应
D.电子对效应
E.康普顿效应
答案
参考答案：B
解析：
乳腺摄影用软X线，管冲压为20～40kV，因其能量低，波长较长，穿透力较弱，主要发生光电效应。
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乳腺摄影主要利用X线的（）。
A.生物效应
B.光电效应
C.散射效应
D.电子对效应
E.康普顿效应
参考答案：B
解析：
乳腺摄影用软X线，管冲压为20～40kV，因其能量低，波长较长，穿透力较弱，主要发生光电效应。
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It was a very cold morning. Some children  were 1 on the ice. It was snowing 2 but they enjoyedthemselves. Mike, the tallest boy, skated fast and he 3 that there was a hole 4 the ice. He 5  into the water. The other children called out loudly for help. 6 at that moment a young worker 7 by and heard them. He put his bike by the side of the river 8 r  an to them. When he pulled Mike out of the 9 , he was all wet. Then he sent Mike to a hospital. 10 that the young man hurried to work. | |||
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