题目

 阅读下面三篇短文，从各小题所给的四个选项中选出能回答所提问题或 完成所给句子的最佳答案。     Mrs. Black lives on Second Street. New Year is coming. She wants to send(寄)  a card to her friend in Toronto, but she doesn’t know where the post office is. She asks her neighbor(邻居) Linda, “ Is there a post office near here? I want to send a card.”   “The post office is far from here,” says Linda, “but you don’t need to go to the post office to post the card. There is a mailbox in front of the supermarket. You can put your carNA表示阿伏加德罗常数，下列说法中正确的是A．H2SO4的摩尔质量是98B．1.7g NH3含有的电子数为NAC．摩尔、质量、时间、长度等是7个基本物理量之一D．22.4L氧气含有的分子数为NA