①在实践中检验分析与综合是否正确　 ②要体现辩证思维的要求　

③要准确地理解分析和综合的辩证关系 ④分析和综合必须是客观的、全面的

    My name is Zhang Peng. I have a friend. His name is John. He has a grandpa and a grandma. They are seventy years old. They are at home. John's father works in a school. His mother is a doctor. John is a good student. They are very busy. They all get up early in the morning. John often helps his grandparents cook breakfast. There is a big garden and many young trees in front of his house. We can play games there. It's great.

用N_A表示阿伏加德罗常数的值，下列叙述中正确的是 (    )