Read the following passage and choose the correct option that best fits each of the numbered blanks.

Urbanisation, which involves the movement of people from rural to urban areas, (16) __________. This has been happening quickly in recent years because people are looking for better jobs, healthcare, and education. Urbanisation has many benefits. Cities often have more job opportunities, which can help people earn more money. They also usually have better transportation, sanitation, and public services, (17) __________ for residents.

However, there are also challenges. Rapid growth can lead to overcrowding, which makes it hard to find enough housing and puts pressure on public services. (18) __________ in some areas. Additionally, more people in cities can lead to more pollution and use up natural resources more quickly. Urban areas might also struggle with traffic congestion, higher crime rates, and (19) __________.

In summary, while urbanisation can bring economic growth and better living conditions, (20) __________ to avoid problems like overcrowding and pollution. Sustainable development, which considers (21) __________, is key to making sure cities grow in a way that benefits everyone.