题目

—Has your brother ever been to Egypt?           —No. He’s been looking forward to the Pyramids.           A. visit             B. visited             C. visits         D. visiting 答案：DNA表示阿伏加德罗常数，下列说法不正确的是（　　）A．64g氧气中含氧分子数为2NAB．1.7gOH-中所含的电子数为NAC．49g硫酸中所含氧原子数为2NAD．58.5g氯化钠中所含的离子数为NA