The correct answer is D. Urbanization
Step-by-step explanation:
In demographics, the word urbanization refers to the increase in the number of people that live in urban zones or cities in comparison to rural zones which commonly occurs as a lot of people leave rural zones and move the cities. Besides this urbanization leads to the expansion and growth of cities and it is related to other factors such as industrialization as factories and industries are located in cities and this makes people that live in rural zones move to cities to find job opportunities and thus urbanization occurs. Also, this concept is the opposite of ruralization in which people move to rural areas and not to cities as in urbanization. Therefore, the mass movement of people to the cities is mainly known as urbanization.