The government has taken some measures to solve the shortage of electricity, but it may be some time __________ the situation improves. A. since B. when C. unless D. before 答案:D13.如图是R原子的结构示意图和磷元素的相关信息,下列有关说法不正确的是( )A.磷元素的相对原子质量为30.97gB.磷原子的核外电子数为15C.R原子在化学反应中容易得到电子D.x的值为8