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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: The vast jungles of the Amazon rainforest are home to tribes mostly isolated from the outside world,whose way of life,largely unchanged for hundreds of years,is now increasingly threatened by modern civilization. Now, scientists discover they can monitor these"uncontacted tribes"using satellites,which would allow inexpensive and safe tracking of these tribes in order to protect them from outside threats. In order to help conserve these uncontacted Indians,researchers need accurate estimates of their populations.One way to collect this data involves flying over their villages,but such overflights are both expensive and could fill these native peoples with fear.Another strategy involves meeting individuals on the ground,but among other risks,scientists could accidentally spread disease to members of the tribes. Instead,scientists investigated whether satellite imaging could monitor uncontacted tribes. The result was inspiring.They confirmed their locations and measured the sizes of their Village,houses and gardens."We can find isolated vinages with remote sensing and study them over time."Walker told Live Science."We can ask:Are they growing?Do they move?" Surprisingly,based on the sizes of the houses and Villages,the scientists find the population densities of these isolated villages are about 10 times greater,on average,than other villages of native Brazilian peoples.This may be due to the fact that they have to live closer together because they are not as good at clearing the forest,since they lack modern devices like chainsaws and tractors,the researchers said.The tribes may also be afraid of spreading out due to fear of being attacked by outsiders,Walker said. The researchers now plan to focus on 29 more isolated villages to"look at their ecology--that is.distance from rivers and roads--and use this to model where else we can find more isolated villages,"Walker said. 
 Answer: Isolated Amazon tribes are monitored with satellites.
Solution:
What is the main idea of the text?