钴60对铅的半值层为10mm，假设在30mm厚的铅板射线源侧辐射剂量为

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问题单项选择题

钴60对铅的半值层为10mm，假设在30mm厚的铅板射线源侧辐射剂量为64R/h，则在其背面应为多少？（）

A、8R/h

B、21.33R/h

C、32R/h

D、16R/h

答案

参考答案：A

选择题

— Got your driving license?

— No. I ________ too busy to have enough practice, so I didn't take the driving test last week.[ ]

A. was

B. am

C. have been

D. had been

单项选择题

使用旋进旋涡流量计时，须保持流量处于流量计所（）的流量范围。

A.覆盖

B.超出

C.相等

D.不同