题目

Before liberation, where floods, earthquakes, fires and many other disasters struck, many people were           to leaving their hometowns.     A. made                    B. intended                C. reduced                 D. forced 答案：C核电荷数小于18的2种元素A、B，A原子最外层电子数为a ，次外层电子数为b；B元素原子M层电子数为a-b，L层电子数为a+b。则元素A是       元素，B是       元素。