题目

There are not many red—crowned cranes today and the number of them ________          getting ________．          A．are；fewer and fewer            B．are；smaller and smaller          C．is；fewer and fewer               D．is；sma]ler and smaller 答案：D 设NA为阿伏加德罗常数的值，下列有关叙述不正确的是（ ）A．标准状况下，1L庚烷完全燃烧所生成的气态产物的分子数为7/22.4NAB．1mol甲基（-CH3）所含的电子总数为9NAC．0.5摩1，3-丁二烯分子中含有C=C双键数为NAD．1mol碳正离子(CH3+)所含的电子总数为8NA