Điền từ thích hợp vào ô trống : Tower running is a sport that involves running up the stairs inside very tall buildings. The first tower running race took place at New York’s Empire State Building in 1978. (1) _____________ there was nothing new about running up tall buildings for fun, this was the first organised race. Nowadays there are tower running races all (2)_____________. There is even a Tower Running World Cup competition. In other types of races, people generally run a (3)_____________ distance. This means that competitors (4)_____________ race on different courses can (5)_____________ times with each other. Obviously, (6)_____________ of these towers are the same; different tall buildings have different numbers of steps. In (7)_____________ to solve this problem, each tower is given a number of points, (8)_____________ on its difficulty. The staircases in tall buildings are usually narrow, with very little (9)_____________ for running. However, when the competitors (10)_____________ the top, they can go outside and enjoy the view!