b. Low-cost computers
With low-cost computers and the arrival of new technologies such as the Internet, people could have greater access to information and could be more interconnected with each other. An example of the impact that it had is the globalization that is being experienced at this moment, all this marks enormous differences between the twentieth century and the twenty-first century.
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.
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.
The correct answer is D. Low-cost computers
The twenty-first century represented multiple changes in comparison to the twentieth century and to the previous centuries, this occurred as the twenty-first century implied globalization processes along with the massive use of technology, advances in science and massive world population grown. One of the main factors that were responsible for these changes was the creation of the computer by the end of the 20th century and then the creation of low-cost computers that were accessible to almost everyone around the world, as this technology allowed people, companies, and governments to be in contact with others all around the world and increased the trade, which lead to globalization and also, the creation of more technological devices. Therefore, from the options provided the one that was most responsible for differences from the twentieth century to the twenty-first century is low-cost computers.