Nowadays, the (0) _____________ common ballon flights are usually for pleasure or sport, but did you know that ballooning began (33) _____________ a science in the 18th century? It all started in 1783, (34) _____________ the Montfolfier brothers were looking (35) _____________ the properties of smoke. What caught their attention was the fact that smoke (36) _____________ make things rise. They experimented for a year or so before they were ready to show their invention (37) ______________ everyone. On their frist attempt, they filled a silk bag (38) _____________ hot air from a fire. The ballon rose more than 1.5 km (39) _____________ the sky. Five month laters, in November 1783, history was made once more when the first flight carrying passengers left the ground. The volunteers took off from Paris and remained in the air for over twenty minutes. Soon afterwards, scientists all over Europe became interested in the potential of ballooning, and it wasn't (40) _____________ before the activity became very popular. (41) _____________ of enthusiastic fans also experimented with ballooning and contributed to its development. Int the 19th century, gas ballooning were used for many different purposes, the most important (42)_____________ being polar exploration. In the twentieth century, hot-air ballooning was re-introduced due to a much improve propane burner. This has (43) _____________ responsible for a whole new generation becoming fond of ballooning either for scientific (44) _____________ sporting reasons.