Answer:
In answer to this very particular question: Which of these is most responsible for differences from the twentieth century to the twenty-first century, I would go for: Kids, social time and education.
Explanation:
The reason for this being my selection comes from seeing how the world today, in the 21st century is totally focused on these three issues. First, most people do not desire to have kids because according to them the world is no longer a good place for raising kids, there is more focus on work-oriented goals, and people want to be free to travel and do other things; kids are perceived as a form of permanency and lack of liberty, so they are not sought as much as in earlier centuries. Social time is the second because today we passed from time with friends and family, face-to -face gatherings, to social time through the virtual world and social media. This has completely changed the way that people today relate with each other. And finally, education. There is a huge focus on education, furthering education, offering more and better, more efficient education, because the world requires people who are better prepared. These are the reasons why I chose the third option.
