某放射性元素的原子核发生两次α衰变和六次β衰变，关于它的原子核的变化，下列说法中正确的是（ ）
A．质子数减小2
B．质子数增加2
C．中子数减小8
D．核子数减小10
设该原子核的质量数（核子数）为m，电荷数（质子数）为n，衰变后的质量数为x，电荷数为y，则有：
m=x+8；n=-6+4+y
由此可知衰变后核子数减小8，质子数减少2，中子数减小10，故BD错误，A正确．
故选A．
| 阅读下面短文，根据短文内容用方框内所给词语的适当形式填空，使短文语义完整。 | |
the daytime. (2)______ this spring, I went outside with my friend Bill (3)______ lived close to me. We were walking to a hill (4)______ I saw a large bright light dancing in the sky. I called Jim and asked him to look up. He kept (5)______, "What is that?" "A UFO!" I shouted excitedly. I (6)______ it was round and red in the center. After we looked at (7)______ for a moment, we found it seemed that it had wings, but it was still round. Bill would not believe me when I told him it (8)______ be a UFO. We shouted (9)______ it and we wished that it would land. We wanted to know (10)______ there was an alien in it. But soon it disappeared. I guessed we scared it off. Do you believe me? It's a true story. |