Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the option that best fits each of the numbered blanks.

Urbanization refers to the process through which cities grow and expand as more people move from rural to urban areas. This phenomenon is driven by various factors, including economic opportunities, educational facilities, and healthcare services, which often attract individuals seeking better living standards. As cities become more populated, they undergo significant transformations in infrastructure, including housing, transportation, and public services.

The rise in urban populations can lead to both positive and negative outcomes. On the positive side, urbanization can stimulate economic development, innovation, and cultural exchange. It often brings improvements in living standards and provides better access to services and amenities. However, rapid urban growth can also strain existing infrastructure, leading to issues such as overcrowding, pollution, and inadequate public services. These challenges can impact the quality of life in urban areas and require careful planning and management.

Effective urban planning is crucial to mitigating the negative effects of urbanization. This includes creating sustainable infrastructure, managing resources efficiently, and ensuring equitable access to services for all residents. By addressing these challenges, cities can harness the benefits of urbanization while improving the overall quality of urban life.

[Adapted from United Nations. "World Urbanization Prospects: The 2018 Revision." United Nations Department of Economic and Social Affairs, Population Division, 2019]

The word they in paragraph 1 refers to ______.