Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 36 to 42.

Two billion tons of solid waste is generated globally per year, and as urban populations continue to grow, many cities are turning to new technologies for cost-effective solutions to clean up waste. “Cities that address waste problems immediately have the best chance to avoid severe long-term consequences,” says Ricardo Cepeda-Márquez, solid waste director for C40 Cities, a global network of cities committed to tackling climate change. Waste that goes uncollected can lead to blocked drains, severe flooding on the street and the spread of waterborne diseases. Additionally, organic matter dumped in landfills generates methane gas, accelerating climate change in the process.

Copenhagen, Denmark, recently opened its innovative waste-to-energy power plant, known as Copenhill or Amager Bakke. The plant, which burns waste instead of fossil fuels, is capable of converting 450,000 tons of trash into energy annually, delivering electricity to 30,000 households and heating to 72,000. Though it still produces CO2 emissions from burning, the city plans to install a system to capture the carbon released and then store this amount of carbon or find a commercial use for it. By tapping an otherwise unused resource, it will also help the city move away from its dependence on fossil fuels. Other cities are also experimenting with similar waste-to-energy plants, but it is warned that a city needs solid infrastructure and a strong waste collection system already in place before it can reap the benefits of one of these plants.

Other cities are starting on a street level, using artificial intelligence and automation to sort recyclables, or sensors to reduce the amount thrown away. For instance, Singapore and Seoul, South Korea, have installed smart, solar-powered trash cans on their streets. Each is equipped with a compactor, enabling it to hold more trash. Once the bin is full, its sensors alert the waste collectors. 

Typically, cities send out different trucks to collect different types of waste - one truck collecting plastic for recycling, another collecting food waste, for example. However, that requires a lot of trucks, which means added costs and more traffic. Norway’ capital Oslo has designed a clever model to circumvent this. Since 2012, city residents have been required to use different colored bags for different types of waste, and instead of collecting them separately, trucks gather all the bags at once and take them to an optical sorting plant. The green bags containing food waste and blue bags with plastic waste are separated from other waste by sophisticated optical reading technology, which detects the color of the bags with approximately 98% precision. The city claims that increased waste segregation and public awareness campaigns have had a positive effect, reducing the amount thrown away by each household and increasing the amount that is reused and recycled. 

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