X线质的表示方法主要有()
A.半价层
B.管电压
C.管电流
D.管电流量
E.阳极靶面物质原子序数
参考答案:A, B
Part 1: Self-introduction
Part 2: Presentation
Part 3: Collaboration
Topic 1:
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Topic 3:
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Topic 5:
每张桌子a元,每把椅子b元,买50套这样的课桌椅,应付______元.