题目

    When I learned that my 71-year-old mother was playing Scrabble – a word game – against herself, I knew I had to do something. My husband suggested we give her a computer to play against. I wasn’t sure my mother was ready for it. After all, it had taken 10 years to persuade her to buy an electric cooker. Even so, we packed up our old computer and delivered it to my parents’ home. And so began my mother’s adventure in the world of computers.     It also marked the beginning of an unusual teaching task for me. I’ve taught people of all ages, but I never thought I wou某元素原子价电子构型3d54S2，其应在周期表（    ）A．第四周期ⅡA族 B．第四周期ⅡB族 C．第四周期ⅦA族 D．第四周期ⅦB族