For example, to understand the characteristics of The US, you need to look at more than one city. Just analyzing New York is not enough because it doesn't reflect the country as a whole. You would have to also look at other major cities such as Chicago, Los Angeles, Atlanta, etc. in order to get a more accurate representation.

It means you need to describe more than one city to answer the question.

"major cities" means the "most important (historically or economically important) / largest / most influential cities. I have visited China, so in my opinion the major cities might include: Shanghai, Beijing, Xi'an, Guangzhou, Chongqing, Chengdu, Hong Kong. Each person will have a different list of "major cities". In a large country like China, there will always be differences between the major cities, such as: food, dialects, history, economy, industry, and culture. China has changed a great deal since 1975. However, most major cities have developed (grown) in similar ways, while keeping some of their unique characteristics. "society = all of the people in China" is made up of a blend (a mixture) of all of their characteristics. So "the most important characteristics of a society" is the combination of all the characteristics of the people who live in the major cities. I hope I haven't bored you by telling you something that you already know:)

Also, I can say this without reservation. Of all the Chinese students I have worked with, those who can speak English the best are those who are from Shanghai.

Jing: I think that if you describe the PLURALITY of Shanghai, you will have a complete subject and you can adequately answer the question.