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In this task, you're given an article and an answer. Your task is to generate the question for the answer based on the given article.

Article: There are a lot of public libraries in Britain. These libraries have more than one hundred and fifteen million books, not including those libraries of public schools. Public libraries not only lend books, music records but also help children, patients in hospitals and others to get special play readings, film shows and so on. The first public libraries were founded in about the year 1850. Today's public libraries usually have a reading-room, a lending room and a reference room. The greatest and most famous library in Britain is that of the British Library in London. It was founded in 1973 and has over 10, 000, 000 books. It has nearly every magazine, newspaper and book published in Britain and other parts across the world. 
 Answer: 10,000,000 or less.
Solution: How many books are there in the British Library?
Why? In the Article, 10,000,000 is mentioned for the number of books available in the British Library, so this is a good question.

New input: Article: Deng Nannan, 15, used to hate drinking milk for breakfast. But she had to drink it because her mom, as well as many others, said that milk was good for her growing body. Besides, milk and bread made up a convenient diet that saved her parents a lot of time after Deng entered junior school and had to arrive at school early in the morning. After that, Mengniu and Yili became her favorite brands of morning milk and yoghurt after dinner. However, she has been forced to change her diet since the recent milk crisis. Many best-selling milk brands such as Mengniu, Yili and Bright were discovered to contain melamine  , which is usually used to make plastic. The bad milk products have sickened more than 5,300 babies and killed four. "I shifted to rice porridge," she said. "My mom has to get up at 5:50 am to prepare my breakfast and make sure that it cools down when I get up." Deng has become addicted to milk, so she doesn't quite enjoy her morning meal these days although she knows that it's a tiring job for her working mom.  "I'll turn back to Mengniu and Yili when they finally improve their products," she said.   However, right now Deng's mom tries to adjust   her eating habits by cooking different foods. Besides rice porridge, noodles, egg soup and soybean milk are prepared as her breakfast. 
 Answer: Because milk becomes more and more expensive.
Solution:
According to the passage, why do some students stop drinking milk?