题目

已知元素X的基态原子最外层电子排布为nsn－1npn＋2，则X元素的原子序数为( ) A.9                B．10               C．17              D．18 答案：【答案】C    ________ being very convenient to shoppers, plastic bags also cause serious white pollution.A. Because                  B. Since                   C. While                   D. If