题目

阅读理解。 Mr. and Mrs. Smith had always spent their summer holidays in New Jersey in the past, staying in a small inn (旅店) at the foot of a hill. One year, however, Mr. Smith made a lot of money in his business, so they decided to go to London and stay at a really good hotel while they went touring around that famous city. They flew to London and arrived at their hotel late one evening. They had expected that they would have to go to bed hungrily, because in that small inn in New Jersey, no meals were served after seven. They were surprised when the waiter asked whether they wA、B、C为三种短周期元素，A、B在同周期， A、C的最低价离子分别为A2－和C－，B2＋和C－具有相同的电子层结构。下列说法中正确的是   (    )A．原子序数：A＞B＞C        B．原子半径：A＞B＞CC．离子半径：A2－＞C－＞B2＋        D．原子核外最外层电子数：A＞C＞B