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.

Example input: 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.
Example output: How many books are there in the British Library?
Example explanation: In the Article, 10,000,000 is mentioned for the number of books available in the British Library, so this is a good question.
Q: Article: Dubai boasts  that it has just built a "new global landmark"---the Dubai Tower, which stands 512.1 meters high now and has just become the tallest building in the world. The Dubai Tower now _ Taiwan's Taipei 101, which is 508 meters tall, and has 141 storeys, more than any other building in the world. The Dubai Tower, being built by South Korea's Samsung Corporation and scheduled for completion next year, is one of a series of great projects taking shape in Dubai. The final projected height of the tower has remained a secret since the project was launched in January 2004; however, it is rumored that the tower will be more than 700 meters tall and have more than 160 storeys. The Dubai Tower has become the tallest building in the world in just 1,276 days, leaving behind other tall buildings. The Dubai Tower will house 30,000 apartments in addition to the world's largest shopping mall. It is the centerpiece  of the 20-billion-dollar venture. Another venture gradually emerging across the desert sands is Dubailand, a series of multi-billion-dollar projects claimed to be the Middle East's very own Orlando. Dubai also paid 100 million dollars to buy the Queen Elizabeth II, one of the world's superb cruise liners , which it plans to turn into a luxury floating hotel. Faced with decreasing oil wealth, the Western-oriented emirate  has raced to turn itself into a business and leisure hub and it aims to more than double the number of tourists to 15 million by 2015. 
 Answer: The Twin Towers
A:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Which building was the tallest in the world before the Dubai Tower began to be built?