核衰变后质量数减少4,原子序数减少2的衰变是()
A.β+衰变
B.β-衰变
C.γ衰变
D.电子俘获
E.α衰变
参考答案:E
解析:旺衰变后原子质量数减少4,原子序数减少2。
Quality audits, reward and recognition systems and information gathering and retrieval systems are tools for______.
A.executing
B.controlling
C.initiating
D.planning
住宅内燃气表高位安装和低位安装位置有哪些要求?