Answer:
The correct answer is D. Cities are so densely populated because they offer a wealth of opportunities for citizens, including jobs, access, education, and healthcare.
Step-by-step explanation:
Cities are the economic and social centers that bring together large amounts of population. In them, work opportunities are concentrated, as they are the place where companies settle, as well as hospitals, schools, universities and other services aimed at improving the quality of life of their inhabitants.
This situation of quality of life means that in turn greater numbers of people wish to move to the cities, in order to take advantage of these job opportunities and the services that are developed in the cities.
As a consequence, large numbers of people constantly move to cities, which increases their population density, making them increasingly populated.