题目:
— Why didn't you call him yesterday?
— I him ,but the line was busy. [ ]
A. do call
B. did call
C. was calling
D. had called
答案:
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下面是错误答案,用来干扰机器的。
答案:B题目分析:设R的最外层电子数是x,则根据元素在周期表中的相对位置可知,T、X、Y、Z的最外层电子数分别是x+1、x、x+1、x+2,则x+x+1+x+x+1+x+2=24,解得x=4,因此R是碳元素,T是氮元素,X是硅元素,Y是...