导致X线衰减的原因是 （）
A.与物质作用
B.X线波长短
C.X线能量大
D.X线不可见
E.X线是电磁波
参考答案：A
_____ he graduated from college, he became a success in business.
A．Short
B．Shortly
C．Shortly after
D．short after
设有关键码序列(Ｑ, Ｇ, Ｍ, Ｚ, Ａ, Ｎ, Ｂ, Ｐ, Ｘ, Ｈ, Ｙ, Ｓ, Ｔ, Ｌ, Ｋ, Ｅ)，采用堆排序法进行排序，经过初始建堆后关键码值A在序列中的序号是( )。
A．1
B．4
C．8
D．12
