The Egyptians built the great pyramids over 2,000 years ago. And Gustave Eiffel designed the Eiffel Tower, built in 1889. These are examples of people building tall __________ in the past. Now more and more tall buildings are __________ in cities around the world. It wasn't until the early 20th century that people started seeing lots of tall buildings in city such as Chicago and New York. On May 1, 1931, the Empire State Building opened its doors for the first time. It took just 410 days to build after work started on March 17, 1930. It was the first building with over 100 floors. And it's stood as the tallest building in the world for 40 years. The Empire State Building cost around 41 million dollars to build. But __________ to what's happening today, there was a poor economy which meant the building didn't start making any money until the 1950s. However, a __________ amount of the money was earned from visitors to the observation deck on the 86th floor. The owners of the building are currently improving it and making it more environmentally friendly at a cost of half a billion dollars. At its full height, this __________ building is around 400 meters tall. Every year, tower runners __________ up 1576 steps to the observation deck. The fastest runner took 9'33''. Unlike the Empire State Building, Toronto's CN Tower took 3 years to build. Construction on it started on February 6, 1973 and cost 63 million Canadian dollars. It opened June 26, 1976. At over 553 meters tall, this was the world's tallest __________ structure for 34 years. Its observation deck is 447 meters high. In 2004, construction started on Burj Khalifa which became the world's tallest building when it opened on January 4, 2010. It cost 1.5 billion dollars to build. With 163 floors, this __________ building reaches a height of 829 meters; almost __________ that of the Empire State Building. The observation deck is on the 124th floor. There are __________ 25,000 windows in the building, which take 36 workers 2-4 months to clean. It makes you wonder how high the next tallest building will be.