题目

NA为阿伏加德罗常数的值，下列说法正确的是(      ) A．0.5mol羟基中所含电子数为5NA B．1mol苯乙烯（）分子中含有碳碳双键的个数为4 NA C．标准状况下，11.2L的二氯甲烷所含的分子数为0.5NA D．常温下，7.8 gNa2O2中含有的离子总数为0.3NA 答案：D –Have you ever traveled abroad? 　　--Sure. I ____ the language of English in the USA two years after I graduated from the university. 　　A. used to learn B. was used to studying C. have studied D. didn’t use to study