Read the following passage about sustainable cities 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 from 18 to 22.

Many cities around the world are striving to become more sustainable in response to pressing environmental challenges. Urban areas consume significant resources and produce large amounts of waste, but cities (18) _______. Some cities have adopted policies to improve air quality, manage waste efficiently, and create green spaces for citizens to enjoy. These initiatives not only enhance the local quality of life but also mitigate the harmful effects of pollution and global warming. For example, Paris has introduced more bicycle lanes to reduce car use, and Singapore has adopted an advanced waste-to-energy system. (19) _______ may also help reduce pollution and promote a healthier lifestyle.

Moreover, innovations in urban planning now aim to reduce energy use and improve public health by redesigning buildings and transportation systems. By creating more sustainable cities, urban areas can help reduce their environmental footprint. For instance, vertical farms are being introduced to grow food in high-density areas, reducing the need to transport goods from rural areas. Additionally, rooftop gardens and other green architecture techniques are increasingly popular for providing insulation and reducing energy costs. New technologies and innovations (20) _______.

One example is the use of renewable energy sources, such as solar and wind power, in urban areas. These energy solutions not only reduce emissions but also provide (21) _______. Furthermore, cities like Copenhagen aim to be carbon-neutral by 2025, setting ambitious goals for themselves that inspire other cities around the world. As cities continue to grow, (22) _______.