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问题 单项选择题

属于剂量限制体系防护基本原则内容的是

A．屏蔽防护

B．缩短受照时间

C．增大射线源距离

D．辐射实践的正当化

E．采用隔室操作检查

答案

参考答案：D

解析：建立剂量限制体系的基本原则包括辐射实践的正当化，防护水平最优化，个人剂量限值。

填空题

Learning in class is a way for students to study. Students sit in the classroom and小题1:to the teacher. Is this the小题2:way for students to learn something? Of course not. There is another way to learn, that is, students can teach小题3:.

How do you teach yourself ? The小题4:thing you must do is reading. Read something you are interested in,小题5:what you have to read. The second is that you must ask yourself小题6:. You can write down the questions. A clever student is usually good at小题7:questions. The third is to answer the questions yourself小题8:thinking hard, by reading the text or other books, and sometimes by asking other people. This is the way of teaching yourself. And you must do all these by yourself. If you keep小题9:like this for a long time, you are sure to小题10:in your study.
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选择题

关于曲线运动，下列说法正确的是（　　）

A．曲线运动不一定是变速运动

B．曲线运动可以是匀速率运动

C．做曲线运动的物体没有加速度

D．曲线运动物体的加速度一定是变化的
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