The correct answer is A. Urban sprawl and crowds moving into the city
Step-by-step explanation:
The "exurbs" are areas placed outside the suburbs that are less crowded that suburbs and whose residents work in areas that are far from the place where they lived. This term emerged in the 1950s in the U.S. as communities that were rural or semi-rural were created beyond the territory of the suburbs; additionally, the creation of the exurbs was mainly caused by the number of people that move from rural areas or other countries to urban area which is known as urban sprawl. This urban sprawl made cities crowded and also expensive and because of this, people who could afford to house in rural or semi-urban areas created exurbs as an alternative that was less crowded and had more space than suburbs. Therefore, the factor that led to the creation of exurbs was the urban sprawl and crowds moving into the city as this motivated people to create communities in "rural areas" that were still close to the city but were not as crowded as suburbs.