Instructions: In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.
Input: Article: A new factory that turns used wine bottles into green sand could revolutionize the recycling industry and help to filter the nation's drinking water. For the last 100 years special high grade white sand quarried at Leighton Buzzard in Bedfordshire has been used to filter tap water to remove bacteria and impurities--but this may no longer be necessary. The green sand has already been successfully tested by water companies and is being used in 50 swimming pools in Scotland to keep the water clean. _ by one million pounds from the European Union and the Department for Environment, Food and Rural Affairs(Defar), a company based in Scotland is building a factory to turn beverage bottles back into the sand from which they were made. The idea is not only to avoid using up increasingly scarce sand in Scotland and avoid any further quarrying but also to solve a crisis in the recycles only 750 000 tones of it. Howard Dryden, the scientist and managing director of the company has spent six years working on what he calls Active Filtration Meadia, or AFM, the recycled glass. He says he needs bottles that have already contained drinkable liquids to be sure that drinking water would not be polluted. "The fact is that tests show that AFM does the job better than glass, it is easier to clean and reuse and has all sorts of properties that make it ideal for other applications, "he claimed. He also thinks the market will be able to take 250 000 tones of green sand a year. The plan is to build five or six factories in cites in UK where the bottles come from to cut down on transport. The factory will be completed this month and is expected to go into full production on January 14 next year. Once it is providing a "regular" product, the government's drinking water inspectorate will be asked to perform tests and approve it for general use by water companies.
Answer: the green sand has been used to keep the water clean
Output:
It may no longer be necessary to use high-grade white sand to keep water clean because _ .